This assumes that they are the only party with standing to sue, which is not likely the case. (Previous rulings on the lack of the authority of the executive to withhold appropriated funds have come in suits by intended recipients.) Both private parties (nonprofits and businesses) [1] and a group of 23 states [2] have already filed suit over the order.
Supreme court is in Trump's pocket. You can bet it will be appealed, all the way up, with some new legal theory invented to say that Trump can do whatever he wants.