IN LATE January 2017, President Trump's first travel ban made for a brash start to the young administration: an aggressive assertion of executive power in service of one of Mr. Trump's most incendiary campaign promises. Almost a year later, the president's promised ban on Muslim entry into the United States is more a story of weakness than of strength. Judge after judge blocked the order from going into effect after finding it likely unlawful. The administration is now battling in court to defend a third, watered-down version of the ban that bears little resemblance to Mr. Trump's original policy, though it remains equally useless and cruel.

The Supreme Court may finally weigh in on the ban's legality in the new year. The high court allowed the order to fully go into effect in early December while federal judges in the U.S. Courts of Appeal for the 4th and 9th Circuits considered whether to halt enforcement of the ban's third iteration. Just before Christmas, the 9th Circuit decided that the executive order went beyond the president's power to control the flow of immigration.

Earlier court rulings cited Mr. Trump's anti- ­Muslim comments as evidence that the travel ban violated constitutional guarantees against religious discrimination. As a matter of policy and morality, those judges were right — but the courts also moved out ahead of settled law by pointing to Mr. Trump's statements from the campaign trail. The 9th Circuit's recent decision takes a more cautious route by focusing instead on whether Congress granted Mr. Trump the authority to issue his latest travel ban.

The third executive order indefinitely limits entry into the United States from five of the majority- ­Muslim countries included in the original ban, along with travel from two non-majority-Muslim countries (Venezuela and North Korea) and one country with a significant Christian minority (Chad). Ninth Circuit judges found that the potentially permanent nature of the barriers to entry went against the statutory scheme laid out by Congress in the Immigration and Nationality Act.

What's more, the court held that the president failed to meet the act's requirement of "finding" based on reason or evidence that travel from the eight countries would harm the United States — rather than simply declaring it to be so. The administration has presented nothing to suggest a connection between a person's nationality and the likelihood of his or her being a threat. In other words, even the weakest version of the travel ban is still vulnerable because Mr. Trump drafted an ideological order by fiat instead of going through the normal processes of governing.

Despite the Supreme Court's request that the 4th and 9th Circuits decide the case briskly, the former court has yet to issue an opinion. Once it does, that may open the door for the Supreme Court to hear arguments on the ban's legality. It's not clear how the justices might rule. What is clear is that the ban is bad policy made poorly. As the 9th Circuit wrote of the order's effect on American Muslims: "It cannot be in the public interest that a portion of this country be made to live in fear."