yeah. the democrats want to argue that declaring a national emergency to get around congress is unconstitutional because it is giving the executive branch control of a financial bill, and they're completely, unequivocally wrong about it. the precise error that they're making is in treating the issue as a criminal case - they are essentially trying to establish a motive.
but, constitutional law is not criminal law, and the president's motives are irrelevant. in fact, not only are they irrelevant, but they are even explicitly outside of the scope of judicial review, by the very same legal clause that they're trying to cite.
what the democrats are imagining would look very different than what trump is actually doing. in order to breach the constitutional rule that the democrats are pointing to, trump would have to literally produce an executive order that gives him control of the country's finances, which would likely be overturned by congress without requiring a court battle.
and, on that note, it is not clear to me that the president has two thirds support in the senate for this. the easiest way to overturn this might be for congress to override the veto.
but, if the argument being produced by the democrats is that he's using a dirty trick to get around congress, then what they're doing is essentially crying foul for being outmanoeuvred. there's a rule against overstepping your bounds, but there's no rule against finding a way around them; that's not unconstitutional, it's just finding a way to govern in a system that is designed to prevent it.
so, if the democrats go in and make this argument that he's trying to circumvent congress, it's not the case that they're wrong. it's rather the case that what they're saying doesn't matter. they might be able to get some pothead in the san francisco circuit to buy their arguments, which are political rather than legal, but as soon as it gets into a real court, the judiciary is going to immediately put a block on any attempt to question the president's motives, because it is beyond the jurisdiction of the judicial branch to do so. the court will need to look at the actual issue at hand, which is whether there is a reasonable grounds for an emergency, and not at some conspiracy theory cooked up by some criminal law attorneys.
if the democrats actually launch this action properly - which is a judicial review case - they could win it with minimal effort. but, if they politicize it into a constitutional law case, and then misapply bad criminal law arguments that have no merit in a constitutional law discussion, they're going to get laughed out of the court room.
again - 2:1 that they fuck it up.
i think they've already broadcasted that they will.