The way the US legal system works is if the US Attorney General tells the US President an act is legal, regardless of if it is, until the Supreme Court or Congress act, the President is free to do as the US Attorney General said.

Under the US Constitution, The President is the Commander in Chief of the military, to not follow a direct order would be a likely be a crime for anyone within the military.

Trumps statements counted as a proclamation, if the US Attorney General said they did.