On the other hand, it also makes a kind of sense. Trump has been taking his campaign promises relatively seriously compared to previous presidents. It may be the reason that judges have been so willing to wink at campaign rhetoric in the past is the sense of, c'mon, it's just talk for the rubes. Nobody's seriously going to do that stuff in office. They just have to say it to get elected.
What happens when somebody comes along who maybe really is going to 'do that stuff in office'? It's easy to understand the panic. Nothing terrifies a cynic more than sincerity.
Nevertheless, I think Powerline has it right (previous link):
The states’ argument is in essence that Trump is a bigot, and thus his winning presidential campaign in fact impeaches him from exercising key constitutional and statutory powers, such as administering the immigration laws.I kind of like the idea that you could elect a partial-president, one whose powers are limited by the flaws in their character. As a purely theoretical idea, it would be great if people who had the right virtues to execute the powers well were the ones entrusted with those powers. If someone without the right virtues was elected, it would be great -- in theory -- if the powers were temporarily entrusted in someone else who had those virtues.
However great this idea is as a pure theory, it's completely impossible in practice. There is no mechanism for making it work other than forcing the executive branch to completely relinquish the relevant power for as long as Trump is president. It's not that, since Trump is a bad guy in certain ways, the courts will delegate the powers to someone else they do trust -- Mattis or whomever. It's that America, not just Trump, would lose the capacity to make national security decisions based on immigration for four years.
That's unworkable. Many people might argue that other bits of campaign rhetoric make Trump unacceptably dangerous as commander in chief. (Indeed, one person who made that argument repeatedly was Hillary Clinton.) So does that mean the courts should prevent him from taking any military actions -- meaning, that America should stop defending herself for four years? Maybe just against the Muslim world, plus China, if those are the areas where Trump's rhetoric was especially explosive?
Obviously that isn't acceptable. Neither is it workable for every executive policy to have to satisfy each of the several hundred Federal judges out there in order to go into effect. This is going to cause problems, though, because the judges appear to be committed to the idea that they should have that power.