I hope trump has a back up plan cause you CAN NOT trust the Mexican government!! I know what I speakth!!!
This was decided by he SCOTUS in Trump v. Hawaii 5/4 No. 17-965, 585 U.S. 2018. stop all immigration for a period he deems necessary.
8 U.S.C. § 1182(f)
Whenever the President finds that the entry of any aliens or of any class of aliens into the United States would be detrimental to the interests of the United States, he may by proclamation, and for such period as he shall deem necessary, suspend the entry of all aliens or any class of aliens as immigrants or non-immigrants, or impose on the entry of aliens any restrictions he may deem to be appropriate.