If indeed the Wall construction begins..
I think impeachment proceedings begin that day. They will scream he is violating a signed agreement. I just dont see doing him this. Damn those bastards for sticking that clause in there but that was the insurance against this move.
National Defense trumps (no pun intended) all.
Impeachment is extremely unlikely before the next congress takes over in January 2019. And if GOP prevails in 2018 election, fuggetaboutit.
They have tried to impeach him already. The motions don’t get to the floor. Barack Obama played fast & loose with Government money and no one said boo. If POTUS does this he will have figured out how to do it legally before he signed the act. Mulvahny would be the guy to have made the plan.
Congress CANNOT order the President NOT to build a wall.
Separation of Powers.
National Defense is owned by the President. Nobody else.