XXX IMG_GTY_182286605_A_POL__1_1_P7J0VJEV.JPG
U.S. Capitol building in Washington, D.C.
Win McNamee, Getty Images

WASHINGTON — With less than six months until Election Day, Democrats remain hopeful a wave will sweep them into power in the U.S. House, Senate or both — but evidence that such a trend is building remains mixed.

Working to their advantage: In some areas, strong Democratic challengers have been outraising incumbent Republicans. Democrats have maintained about a 6-point edge in the FiveThirtyEight.com average of generic partisan preference polls for Congress. All of Pennsylvania’s districts have been redrawn by the state Supreme Court, which could make as many as a half-dozen more favorable to Democrats. And President Donald Trump’s disapproval ratings are still above 50%, never a good sign for a president’s party.

But despite that, the generic poll has barely moved in three months.

Republican incumbents in key states like California, New York and Florida look strong. And Trump’s job approval, while still bad, has been getting better. Also good news for the GOP: The emergence of Martha McSally in Arizona’s Senate race, the withdrawal of Danny Tarkanian’s challenge to U.S. Sen. Dean Heller of Nevada, and a win by West Virginia Attorney General Patrick Morrisey as the Republican nominee to take on Democratic U.S. Sen. Joe Manchin.

And with primaries filling the calendar through August, the political season is just getting started.

“I think the environment overall favors Democrats. The question is, ‘How do you define a wave?’ ” said Jennifer Duffy, senior editor for the Cook Political Report, which handicaps races. “Right now, it doesn’t look like it’s going to be a wave of enormous proportions, but it’s still early.”

More: Women are winning, but Dems' division still there: Takeaways from Tuesday's primary

Opinion: Never Trump Republican's midterm plea to Democrats: Reach out to people like me

To take back the majority in the 435-member House, Democrats need to flip 23 seats currently or most recently held by Republicans. To take back the Senate, they need to gain only two seats — though it’s considered a harder task because they have to do so while holding on to 24 currently held by their party or those aligned with it, including 10 in states where Trump won in 2016.

Earlier this year, the USA TODAY Network compiled a list of 25 bellwether races in 14 states across the country which could over time help predict whether Democrats are riding a wave or whether Republicans can maintain their majorities in Congress. Since then, some things have changed — the new Pennsylvania maps, for one thing, meant new districts, and House Speaker Paul Ryan’s retirement convinced us to add his Wisconsin district to the list (so now there are 26).

With some primaries underway, we took a fresh look at the state of the races, which we’ll continue to monitor through Election Day.

ARIZONA

930254866 E ACE ENT CEL USA CA
Rep. Kyrsten Sinema, D-Ariz., speaks at a Human Rights Campaign dinner at the JW Marriott Los Angeles on March 10, 2018.
Rich Fury, Getty Images for Human Rights Campaign

Senate (open):The race to replace Republican U.S. Sen. Jeff Flake in a state won by Trump by only 3-½ points hasn’t changed much: U.S. Reps. Martha McSally, a Republican, and Kyrsten Sinema, a Democrat, are the favorites to square off in the fall.

Former Maricopa County Sheriff Joe Arpaio and former state Sen. Kelli Ward remain potential factors in the Aug. 28 Republican primary, but neither has managed to break through with significant fundraising or key endorsements. By contrast, McSally had $2.6 million in cash on hand as of March 31; Sinema, who joined the race four months earlier, had about $6.8 million in cash available. Former Gov. Jan Brewer recently endorsed McSally, which could help consolidate support among immigration hardliners.

More: Sen. Jeff Flake says he will not seek re-election in 2018, citing nastiness of Trump-era politics

XXX MCSALLY_4.JPG USA AZ
Rep. Martha McSally, R-Ariz, speaks at the grand re-opening of a veterans center at the University of Arizona, Monday, August 21, 2017.
Tom Tingle, The Arizona Republic

2nd District (open): McSally’s open seat in southeastern Arizona is still a pick-up opportunity for Democrats.

Former U.S. Rep. Ann Kirkpatrick had more than $820,000 in cash available at the end of March, well ahead of Matt Heinz, the 2016 Democratic nominee. Meanwhile, Mary Matiella, a former Pentagon official, has gotten the endorsement of U.S. Rep. Raul Grijalva, D-Ariz. The Republican frontrunner is Lea Marquez Peterson, the Tucson Hispanic Chamber of Commerce president and CEO. She is expected to receive significant help from outside groups if she wins the primary. Also of note: With new U.S. Rep. Debbie Lesko, a Republican, winning a recent special election in a heavily GOP district by less than 5 percentage points, it could mean other Arizona districts are up for grabs that previously were considered safe for Republicans.

CALIFORNIA

39th District (open): Republican U.S. Rep. Ed Royce is stepping down in an Orange County district considered a key indicator of a potential Democratic wave.

AP NORTH KOREA WEAPONIZING THE DOLLAR I FILE USA DC
House Foreign Affairs Committee Chairman Ed Royce, R-Calif. speaks on Capitol Hill in Washington.
Carolyn Kaster, AP

But Democrats are worried that with 10 candidates in the June 5 primary — and the top two vote-getters facing off regardless of party affiliation — that their chances of fielding the strongest candidate may be hurt. Businessman Andy Thorburn and philanthropist Gil Cisneros have raised the most money: more than $2 million each, largely due to loans they’ve given their campaigns. Pediatrician Mai-Khanh Tran has raised more than $1 million. On the Republican side, former state assembly member Young Kim has out-raised five other GOP candidates and won Royce’s endorsement.

45th District (Mimi Walters, R): The state Democratic Party endorsed law professor Dave Min to be the nominee in the race to unseat Walters in an Orange County district that Trump lost in 2016. But Min has competition: Both former Obama administration staffer Brian Forde and another law professor, Katie Porter, have outraised Min, and a couple other Democrats are also in the race. Meanwhile, Walters is no pushover: She’s been targeting female voters with ads supporting sexual assault victims while also hitting conservative issues like border security. The Cook Political Report lists the district as “likely Republican,” predicting Walters will keep her seat.

FLORIDA

18th District (Brian Mast, R): Mast, a first-term congressman holding a seat previously held by a Democrat, drew two challengers in the Aug. 28 Republican primary after a mass shooting at a high school in Parkland, Fla. Mast said he supported a 60-day moratorium on assault weapon sales, causing challengers real estate entrepreneur Dave Cummings and physician Mark Freeman to accuse him of abandoning the “Trump agenda.” Mast is still seen as having the edge in both the primary and the general. Two Democrats are vying for the chance to face him: Former Obama administration adviser Lauren Baer, who has key backing from Democratic officials, and Navy veteran and lawyer Pam Keith, who has accused Democratic Party leaders of trying to rig the race in Baer’s favor.

INDIANA

XXX IMG_AP_SEN_DONNELLY_RE_E_1_1_52JIQQ71.JPG
Sen. Joe Donnelly, D-Ind., takes questions from the media on Aug. 21, 2017, in Anderson, Ind.
Don Knight, AP

Senate (Joe Donnelly, D): In a race that Republicans are looking at as a prime Senate pickup in a state that Trump won by 19 points, Donnelly is positioning himself as a moderate and hoping he can attract enough crossover votes to win.

He wasn’t hurt by a fractious Republican primary that concluded May 8 with wealthy businessman and former state Rep. Mike Braun beating two sitting congressmen for the GOP nomination.  Democratic-aligned groups are already using some of the charges leveled at Braun in the primary against him. But Trump clearly plans to use his popularity in the state — and the fact that Vice President Mike Pence was the state’s governor — to his party’s advantage: He went to Elkhart on May 10 to stump for Braun and gave Donnelly a new nickname, “Sleepin’ Joe.”

IOWA

1st District (Rod Blum, R): Democrats view this as a possible pickup, since a poll late last year showed the party as having a big generic-ballot advantage. Some handicappers have it as a toss-up. Outside groups have started to pay some attention to this rural northeastern Iowa district, too, though they haven’t spent much cash yet or made significant television buys. Blum won his last race by 8 percentage points and will face one of four Democrats running in a June 5 primary, one of whom, state Rep. Abby Finkenauer of Dubuque, has raised nearly $1.1 million and as of March 31 had about $730,000 on hand. That’s less than Blum’s $1.4 million but a lot more than any of the other Democrats.

3rd District (David Young, R): Young easily won in 2016, but this district — covering Des Moines and southwestern Iowa — includes a sizeable number of urban and suburban voters that Democrats are counting on turning out if they’re going to ride a wave nationwide. Young still has the edge, however. He has a huge fundraising advantage, with more than $1 million on hand as of March 31, compared to about $335,000 for Eddie Mauro, a businessman and former teacher running for the Democratic nomination. Mauro also must contend with a primary field that includes businesswoman Cindy Axne and Pete D'Alessandro, a community organizer who worked on Bernie Sanders’ presidential campaign — though this, too, could be a race that attracts significant outside money once the nomination is settled.

KENTUCKY

6th District (Andy Barr, R): With primaries next Tuesday, Lexington Mayor Jim Gray and former U.S. Marine pilot Amy McGrath are breaking the bank for the chance to be the Democrat to take on Barr. Gray has spent upwards of $400,000 on advertising since entering the race, and McGrath, whose initial campaign ad went viral, has spent nearly $600,000, according to the Lexington Herald Leader. Democrats have won this district as recently as 2010, but were blown out in the past two House elections. With a strong field of Democratic contenders — and a district centered on Lexington and the University of Kentucky — party faithful believe they might have a chance. Barr still has the fundraising edge, however, having raised about $2.5 million to McGrath’s $2 million (much of which has been spent on the primary).

MICHIGAN

8th District (Mike Bishop, R): The Cook Political Report says this is a “Lean Republican” race in a district spreading west from the northern Detroit suburbs to Lansing. But Elissa Slotkin, a former intelligence officer and Defense Department official, has continued to outraise the incumbent and, as of March 31, had about $40,000 more on hand than he did. Bishop has worked to define Slotkin as more of a D.C. resident than a Michigander, but so far, it hasn’t seemed to hurt her as she continues to generate national buzz. Bishop even caught a little-known opponent in the Aug. 7 primary in businessman Lokesh Kumar. Slotkin, meanwhile, still faces a Democratic opponent in professor Chris Smith.

11th District (open): How wide open is this race? Fourteen candidates — six Republicans, six Democrats, a Libertarian and an independent — have filed to run for this suburban Detroit district being vacated by U.S. Rep. Dave Trott, R-Birmingham. Democrats smell blood here. On the Republican side, businesswoman Lena Epstein has poured almost $1 million into her race but faces a field that includes former U.S. Rep. Kerry Bentivolio, state Sen. Mike Kowall, state Rep. Klint Kesto and former state Rep. Rocky Raczkowski. The Democratic field is just as unsettled: state Rep. Tim Greimel has the experience, but entrepreneur Suneel Gupta has raised $1 million, followed closely by former Obama administration official Haley Stevens. Expect outside money to flood in once the nominations are settled.

NEVADA

Senate (Dean Heller, R): Heller, the Senate’s most vulnerable Republican, can breathe a little easier heading into the June 12 primary with Danny Tarkanian dropping his bid for the GOP nomination at Trump’s request.

XXX IMG_AP_US_SENATE_NEVADA__1_1_52JIQQ5L.JPG
Sen. Dean Heller, R-Nev., answers a question during a town hall in Reno, Nev., on April 17, 2017.
Andy Barron, AP

But Heller is still at a fundraising disadvantage to his top Democratic foe, U.S. Rep. Jacky Rosen, who collected twice as much as he did during the first three months of the year and has outraised him $7.7 million to $6.1 million. Both face primary opponents, but none of them are considered likely to knock off the better-known candidates. The good news for Republicans headed into the general election this fall is that Democrats have lost some 20,000 active voters since January, compared to about 6,000 Republicans.

More: Heller loses primary challenger after Trump urges Tarkanian to run for House

NEW JERSEY

7th District (Leonard Lance, R): Lance won re-election by 11 points in 2016, but he’s still considered the state’s most vulnerable incumbent in a district that went for Hillary Clinton. A Monmouth University poll in April showed that Democrats had a 19-point margin in generic preference statewide, with much of the increase coming from traditionally Republican districts like this one. Lance has been touting his bipartisan credentials in an attempt to shore up his standing. But several Democrats are vying for the nomination in June 5 primary, including Lance’s 2016 opponent, Peter Jacob, who has a group of Bernie Sanders supporters behind him. County leaders, meanwhile, are backing Tom Malinowski, a former Obama administration official who has a big fundraising lead over Jacob and the other Democrats.

11th District (open): There’s plenty of drama in this northern New Jersey seat being vacated by U.S. Rep. Rodney Frelinghuysen: A couple of Republican chairmen recruited financial adviser Antony Ghee to run against Assemblyman Jay Webber, who’s getting plaudits from conservative groups. But Ghee only joined the party officially the day before starting his campaign. Some anti-Webber forces convinced businessman Peter De Neufville to jump into the race on April 2, the filing deadline. Meanwhile, the Democratic field in this tossup election is dominated by Mikie Sherrill, a Navy veteran and former prosecutor who has raised more than $2.3 million, far more than anyone else. There are rumblings from others, however, that national Democrats are trying to “rig the primary process” for Sherrill and other chosen candidates.

NEW YORK

1st District (Lee Zeldin, R): This is a Long Island district that Trump handily won, but if a wave is coming, it may strike here considering the mix of wealthy and middle-class suburban areas that make it up. Democrats are clearly eyeing the seat, with five candidates vying for the right to challenge Zeldin — a two-term incumbent — in November. Party leaders have largely coalesced around Kate Browning, a Suffolk County legislator who has gained the backing of powerful U.S. Rep. Joseph Crowley. But businessman Perry Gershon has raised the most money of the Democratic hopefuls — more than $1.4 million, with about $600,000 of that in the form of a loan to himself — compared to less than $400,000 for Browning. The Cook Political Report, meanwhile, considers this a “Likely Republican” seat for now.

19th District (John Faso, R): Trump won by 7 points here, and Faso did slightly better than that in his first race in 2016. So why is this race through the Hudson Valley considered a tossup by some? Because former President Barack Obama won here twice, and a field of qualified Democratic candidates has emerged. Six Democrats are vying for the party’s nod in the June 26 primary, including Gareth Rhodes, who worked for the Cuomo administration, attorney Antonio Delgado and entrepreneur Brian Flynn. Delgado, Flynn and Patrick Ryan, a small-business owner, have all topped the $1 million mark in fundraising. (Delgado was at $1.9 million as of March 31, having outmatched Faso’s own $1.7 million). Meanwhile a former “Law & Order” actress, Diane Neal, is running as an independent.

24th District (John Katko, R): In this district along Lake Ontario, Katko is a target for the simple reason that Hillary Clinton won here by 4 points in 2016 and Obama won here in 2008 and 2012. But Katko, a former federal prosecutor, won handily in the last two elections and may have caught a break when former Syracuse Mayor Stephanie Miner ruled out a run. Now Katko could face the candidate who lost to Miner. Juanita Perez Williams had been in jeopardy of being thrown off the ballot because of a court challenge to her nominating petitions. But the lawsuit was withdrawn, and she now faces Dana Balter in the primary. Neither has raised much money, however, compared to Katko, who had $1.2 million in the bank.

OHIO

1st District (Steve Chabot, R): If recent events are any indication, it’s going to be a nasty race in this southwest Ohio district. Within a week of 35-year-old Aftab Pureval, the Democratic Hamilton County Clerk of Courts, entering the race, Chabot questioned whether Pureval lived in the district. Pureval’s fiancée filed a police report after she got concerned that a member of Chabot’s campaign was outside their home. Chabot has acknowledged this could be a tough race and, with both having sailed through the primary, Pureval has outraised the incumbent by about $748,000 to $619,000 (though Chabot has much more cash on hand). Democratic groups say this is one of their top targets, and outside groups have been hitting Chabot for opposing the Affordable Care Act.

12th District (open, special election): In the May 8 primary for a special election to this central Ohio district, the establishment Republican candidate, state Sen. Troy Balderson, won a narrow 1-point victory over township trustee Melanie Leneghan. Balderson was backed by former U.S. Rep. Pat Tiberi, while Leneghan had the backing of the Freedom Caucus’ U.S. Rep. Jim Jordan. The win sends Balderson against Democrat Danny O’Connor, the Franklin County recorder, in a special election on Aug. 7 to fill the remainder of Tiberi’s term. While the suburban Columbus district has been reliably Republican, the Cook Political Report calls this race a tossup, with Democrats hoping to capitalize on anti-Trump sentiments.

PENNSYLVANIA

1st District (Brian Fitzpatrick, R): The state Supreme Court’s redrawing of the congressional map this winter made several districts more competitive for Democrats. But this one in eastern Pennsylvania — what is currently the 8th — was already considered about evenly split. Now Democrats should have a slightly larger edge. And if a blue wave is coming, Fitzpatrick, who easily won the primary Tuesday, should be in trouble. He’ll face wealthy philanthropist Scott Wallace, who won a divisive race against former Navy prosecutor Rachel Reddick as the two bickered over residency and partisan backgrounds. Wallace put $2.5 million of his own money in the race but spent most of it in the primary.

More: Trump prompts Dem women to run for Congress in Pa., but they face 'old boys network'

More: Conor Lamb sworn in as Pennsylvania representative after upset victory

7th District (open): Initially, we had the 6th district on this list, a Republican-represented district that slightly favored Hillary Clinton. Now, as reconstituted, it voted for her by a lot. Since that should be a Democratic pickup even in a non-wave year, we’re substituting the open seat in the 7th district, anchored in Allentown. Moderate Republican U.S. Rep. Charlie Dent stepped down, and the race to replace him has been fierce in a district that, as newly constituted, should be about a tossup. In the Democratic primary, former Allentown city solicitor Susan Wild eked out a 1,400-vote win over immigration hardliner and Northampton County District Attorney John Morganelli in a six-person race. On the Republican side, Lehigh County Commissioner and Olympic gold medal cyclist Marty Nothstein beat Dean Browning by just over 300 votes.

17th District: (Keith Rothfus, R): What had been the safely Republican 12th district in western Pennsylvania is now the reconstituted 17th, trading large tracts of conservative-friendly rural areas for suburban sections closer to Pittsburgh. U.S. Rep. Conor Lamb — who just won a stunning bellwether special election in the neighboring and Trump-friendly 18th-soon-to-be 14th — is the Democratic nominee here (he lives in the new district) against the Republican Rothfus, who finds himself in a district that only backed Trump by about 2-½ points over Clinton in 2016, compared to the 21 points his old district did. He’s facing a candidate who has received virtually nonstop coverage in recent months. Both candidates have plenty of money, with Rothfus reporting $1.6 million on hand in late April; Lamb, $1.8 million.

TENNESSEE

GTY 950449738 A POL GOV USA DC
Sen. Bob Corker, R-Tenn.
Alex Wong, Getty Images

Senate (open): The race to replace Republican U.S. Sen. Bob Corker, who decided not to seek a third term, appears to be between Republican U.S. Rep. Marsha Blackburn and Democratic former governor Phil Bredesen, with both facing nominal opposition in their parties’ Aug. 2 primaries.

Beyond that, nothing is certain: Even though Trump won Tennessee by 26 points, a mid-April poll from Mason-Dixon has it as a dead-heat, while other polls show either of the two ahead. It’s being taken seriously, with Trump headed in for a fundraiser for Blackburn on May 29. Meanwhile, Corker has publicly announced his support for Blackburn but won’t actively campaign against Bredesen — who, like Corker, is a former mayor. The two are longtime friends and have worked on a host of projects together.

More: Sen. Bob Corker is standing by his decision not to seek re-election, a senior adviser says

WISCONSIN

Senate (Tammy Baldwin, D): Considered one of several vulnerable Democratic U.S. senators, Baldwin has been putting a personal touch on the race, with a series of television ads on local issues, from her efforts to reverse regulations prohibiting the use of wooden boards in the aging of cheese to the closure of a paper mill.

AP SENATE DEMOCRATS TRADE A USA DC
Sen. Tammy Baldwin, D-Wis., right, accompanied by, from left, Senate Minority Leader Chuck Schumer of N.Y., Sen. Debbie Stabenow, D-Mich., and Sen. Bob Casey, D-Pa., speaks on Capitol Hill in Washington, Wednesday, Aug. 2, 2017, to unveil "A Better Deal On Trade and Jobs."
Manuel Balce Ceneta, AP

In one dramatic spot on the opioid crisis, she shared the story of her late mother's addiction to prescription drugs and battle with mental illness. On the Republican side, Leah Vukmir, a long-time party activist and legislator, earned the endorsement Saturday at the state Republican Party convention. But Vukmir's rival, businessman and U.S. Marine veteran Kevin Nicholson, has vowed to press on to the Aug. 14 primary.

1st District (open): We’ve added this to our list of bellwether districts because its current occupant, House Speaker Paul Ryan, is not running for re-election. It appears Democrats might be able to make a run at this symbolic Wisconsin seat, which has been in GOP hands for almost a quarter-century. Bryan Steil, a former Ryan aide and attorney, has emerged as the top Republican contender in the Aug. 14 primary, and in his first week as a candidate, raised $250,000. On the Democratic side, Randy Bryce, an iron worker who became a progressive star after initially challenging Ryan, is locked in a primary battle against Cathy Myers, a school teacher. Bryce has the fundraising edge, with an amazing $4.8 million compared to Meyers’ $772,000.

6th District (Glenn Grothman, R): Grothman’s race could be a key indicator, given that he’s a two-term incumbent in a district that backed Trump by a 17-point margin and hasn’t elected a Democrat since the 1960s. But some — including Grothman — think he could face a hard race in this rural-suburban district in northeastern Wisconsin. Democratic challenger Dan Kohl, the nephew of former Sen. Herb Kohl, has already raised more than $1.2 million compared to just under $1 million for Grothman, which could point to a tough campaign. Seeking to forge credentials as a centrist, Kohl also made clear in late April that if elected and Democrats regain the majority in the U.S. House of Representatives, he would not vote for Nancy Pelosi as House speaker.

Contributing: Ronald Hansen, The Arizona Republic; Herb Jackson, The (Bergen County, N.J.) Record; Jessie Balmert, Chrissie Thompson and Scott Wartman, The Cincinnati Enquirer; The Des Moines Register staff; Corinne Kennedy, The (Palm Springs, Calif.) Desert Sun; Todd Spangler, Detroit Free Press; Ali Schmitz, Gannett Florida and TC Palm; Maureen Groppe, Gannett Washington and the Indianapolis Star; Thomas Novelly, Louisville Courier Journal; Bill Glauber, Milwaukee Journal Sentinel; James DeHaven, Reno Gazette Journal; Duane Gang, The Tennessean; Joseph Spector, USA TODAY Network Albany Bureau Chief; Eliza Collins, USA TODAY; and Ed Mahon and Candy Woodall, York (Pa.) Daily Record.

Follow Todd Spangler on Twitter: @tsspangler