Let's assume that tomorrow, Trump declares a national emergency under the authority of 50 USX 1501.
On the surface, it let's him build his wall, without congressional approval..
It does so under the authorities of:
It let's him build the wall, let's him replace civil servants with contractors, and let's him make his friends rich..
But it also gets worse, much much worse:
"Injuring, interfering with, or obstructing the preparation for, or carrying out of, war or defense activities, of the United States, or associated countries, with the intent to do so, or reason to believe the actions will do so, punishable with fine....
In short, with one sweep of the pen, by declaring a national emergency... Trump becomes the defacto dictator and can imprison anyone who gets in his way.
So this is unlikely and would be a field day, for years in court.
But also, under the USC, is possible.
This is what happens when you don't sleep.