And here is the fun part. Trump can veto this. Its untested as to whether that is legal. And Brett Kavanaugh will have the final say
OT : I'm all for national emergency declaration. What better way for President Sanders to implement Medicare for All and the new Green Deal in 2021 ? And, unlike the wall, they definitely are national emergencies.
Indeed. Summary:
Yes, The President Can Declare A 'National Emergency' To Build A Wall
It'll be a mess, but the short of it is it'll get tied up in the courts injunctioned before anything can actually be done.
What matters, though, is.... does the government get reopened? Walls are nice political theatre, but the wall itself isn't a significant macro mover. A government shutdown is a huge one.