No, the opposite. The legal waters are rather murky, with ONE test case where the SCOTA denied Harry Truman his attempt to nationalize the steel industry during the Korean War. I have read interpretations of that decision in this current situation and what is clear is that it won't happen fast.
There are several hundred NGO's who would all sue, then the landowners, all Texans, rich and armed who have already told Fox and NBC Trump will "never get my land"
There are a myriad of issues and one precedent, where SCOTA denied Truman his bid to take over the steel industry because of the "national emergency" of the Korean war. What I have read it is a very conclusive ruling, but old enough a judge might be persuaded to have a second look. There is also the issue of States rights and whether the Fed can simply walk in and build a wall.
Then you have environmentalists who would be well armed demanding and likely getting delays while the impact on the animal population, erosion issues etc. have been well studied.
Then you have the states, but I am pretty sure the Feds can't simply send in the Army Corps of Engineers and do what they want.
Anyone of those could hold up construction two to five years, by then what's Trump?
I contend him declaring a national emergency, which he would have to prove in court with reliable figures on illegals and drugs, would be the biggest mistake of any modern president.
Unless you want war in the streets, because that would be the next step