That is the problem with you kids, these days. You run to the founding document when you think it will work for you-like McCabe trying a coup based on the 25th Amendment. Other than that, the Constitution might as well not exist. Unfortunately, for you, Trump is on a solid legal ground, but don't worry, the SCOTUS will get a say, too.
Tell that to the strict constructionists Donny appointed to replace Scalia and Kennedy. The lawyers in his 4000 and some lawsuits also told him he was on solid legal ground, and he lost a good few of those over the years. It's what he pays them to say.
I'd put my money on the actual judges deciding in favour of the C-word, a law they'll still have to interpret and enforce long after Donny's a sad memory. And if they say he can rule by decree like the tinpot dictator he aspires to be, they 're savvy enough to know so can any Democratic whacko when it's their turn at Donny's job. Some elected Republicans still have brains to think that far ahead, as well.
Even though he's pretending this decades old sore-spot he did nothing about for two years is now an 'emergency' (because it threatens the US government with shutdown?) I'd also bet that a good few GOP Senators have enough integrity to insist that it is Congress who decidess what money gets spent how, and where. Not a guy who spends his days in the White House whacking golf balls at a $50,000 computer-screen.
That is what the Constitution clearly says, and Congress has had to legalize the actions of previous Presidents who actually did face real emergencies. If they did not, such massive mis-appropriation of funds would most definitely qualify as a crime or misdemeanour high enough to trigger impeachment.
Anyone think this Congress will be swift to legalize his crack-brained call?