WASHINGTON – If Congress and the White House don't make a deal this week to stave off a partial government shutdown, Saturday – three days before Christmas – could be the start of the third shutdown since President Trump took office less than two years ago.

It's a Saturday in the middle of a more than weeklong holiday season. Will you have to worry whether presents and relatives can make the journey without problems?

The U.S. Postal Service anticipates that Monday will be its busiest day online, which would allow most priority and first-class to reach its destination by Thursday before any possibility of a shutdown. If you mail later than that, know that the Postal Service is an independent agency, so it won't be affected in any government shutdown.

Peak travel is expected to hit Thursday, according to the American Automobile Association. That's also when Congress members want to get out of town and be finished with their work for the year.

Even if Congress can't stop another federal shutdown, air-traffic controllers still will be on the job after midnight Friday, and customs and border agents will continue working at border crossings.

Amtrak, a government-owned corporation, also will operate as usual.

The president traditionally decides whether federal workers get a paid holiday on Christmas Eve, this year on a Monday, according to FEDweek newsletter. President George W. Bush did so in 2001 and 2007; President Barack Obama also did in 2012.

If a shutdown occurs, federal employees deemed nonessential could get that day off anyway. Back pay is never guaranteed when the government is shuttered, but Congress previously has included that provision in its debt-ceiling bills.

Those who want to go to national parks and federally operated museums could find popular places closed or hours curtailed.

During the Jan. 20-22 shutdown, gates at national parks remained open for people to enter but few staff were on hand to protect visitors and park resources.

Buildings, such as visitor centers, were shuttered, and sometimes that included restrooms, according to the National Parks Conservation Association. The Statue of Liberty and Ellis Island initially closed, but the state of New York stepped in on the third day with $65,000 a day to reopen the popular tourist attraction.

Earlier this year, the Smithsonian Institution museums, which include the National Museum of the American Indian and Cooper Hewitt Smithsonian Design Museum in New York, used a rainy-day surplus fund to keep their doors open. In 1995 during the Clinton administration, the National Zoo and museums, which now number 19, were closed to the public for six days. (Never fear: The zoo's animal caretakers always are considered essential.)

Holiday parties also are safe: Food-safety inspections continue but could be curtailed if a shutdown lingers.

The same goes for the Centers for Disease Control and Prevention's ability to react to health emergencies, such as the continuing measles outbreaks in New Jersey and New York. New grants for communities, such as those for Head Start and children's welfare services, also could be delayed, but that's not likely unless a shutdown lingers.

And even with a shutdown, Social Security benefits still go out, as will Medicare services and benefits from programs such as the Supplemental Nutritional Assistance Program and Women, Infants and Children for at least as long as some carryover money in the states or the federal accounts are available.

A version of this story was published Jan. 20. Follow Todd Spangler on Twitter: @tsspangler