President Trump's effort to restrict travel from six predominantly Muslim countries suffered another in a string of setbacks Monday when a second federal appeals court said it discriminated based on nationality and exceeded his authority.

The U.S. Court of Appeals for the 9th Circuit, an overwhelmingly liberal court, ruled unanimously that the temporary travel ban should remain on hold — the final judicial blow as attorneys prepare for a likely showdown before the Supreme Court.

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"The Immigration and Nationality Act gives the president broad powers to control the entry of aliens, and to take actions to protect the American public. But immigration, even for the president, is not a one-person show," a three-judge panel declared.

"The order does not offer a sufficient justification to suspend the entry of more than 180 million people on the basis of nationality. National security is not a 'talismanic incantation' that, once invoked, can support any and all exercise of executive power."

The court found that revisions made by the White House did not eliminate the underlying problems of the ban, which targets six majority-Muslim countries: that it discriminates, whether by religion (as other courts have ruled) or nationality, and exceeds the president's authority. The appeals court, which also ruled against Trump's first travel ban in February, concluded that his own statements made clear that the revised version contains the same flaw by targeting Muslims.

"The president must make a sufficient finding that the entry of these classes of people would be 'detrimental to the interests of the United States,'” the panel ruled. "Further, the order runs afoul of other provisions ... that prohibit nationality-based discrimination and require the president to follow a specific process when setting the annual cap on the admission of refugees."

At issue is Trump's proposal to ban most travel from Iran, Libya, Somalia, Sudan, Syria and Yemen for 90 days and suspend the entire refugee program for 120 days. Justice Department lawyers made several adjustments from the first travel ban to address concerns raised by judges across the country. The revised version allowed current visa and green card holders to continue traveling, removed Iraq from the list of targeted countries and deleted a section that gave preference to Christian minorities in those countries.

Trump has said the travel ban is needed to give the federal government time to develop enhanced vetting procedures for people coming from terror-prone countries to ensure terrorists don't sneak into the United States through the legal immigration system. Critics have said the orders amount to an unconstitutional "Muslim ban" that Trump called for during his presidential campaign.

Trump has insisted the ban is legal and questioned his own lawyers for bowing to court rulings by issuing a "watered-down" version that was also blocked by courts. In a series of tweets last week, the president said the Justice Department should have stuck by the original travel ban and pushed for a "much tougher version." He continued a series of attacks against judges who have ruled against him, tweeting that "courts are slow and political!"

The revised ban already had been blocked by federal district court judges in Hawaii and Maryland and by the U.S. Court of Appeals for the 4th Circuit, based in Virginia. The Justice Department filed an appeal with the Supreme Court, which is expected to announce in the coming weeks whether it will hear the case.