It would fall to the U.S. Marshals Service — which is part of the Department of Justice — to enforce a judge’s order. But “if Trump wanted to fully not comply, he could direct the Department of Justice not to comply. At that point, you have a full-on constitutional crisis,” Gertner said.

“Congress, ultimately, is the arm of our government that enacts statutes. And if the president is claiming authority under a statute to do X and Congress disagrees, Congress can amend the statute and say, you don’t have the power,” she said.

However, Republicans, faithful to Trump, control both the House and Senate, so opposition is unlikely.