This has become the go-to tactic of the left in the Trump era: When the president exercises any sort of executive authority whatsoever, all you have to do is find a liberal federal judge who is willing to rule Trump’s action illegal.
Often these judges have no authority to even get involved with these cases (looking at you, Judge Derrick Watson), but ties up the administration and forces them to file appeals – often taking them all the way to the Supreme Court where the White House inevitably wins – thus exceedingly complicating the process of governing.