Forget unconstitutionality and crime, the guy is a flat out harcore blatant traitor and he should be removed from office ASAP, tried for treason and executed if found guilty. The code is extremely clear on that...
18 U.S. Code § 2381 - Treason
Whoever, owing allegiance to the United States, levies war against them or adheres to their enemies, giving them aid and comfort within the United States or elsewhere, is guilty of treason and shall suffer death, or shall be imprisoned not less than five years and fined under this title but not less than $10,000; and shall be incapable of holding any office under the United States.