Der Fuehrer maintained (somewhat correctly) that he can do all of this without congressional authority, at least for a while. The backlash against action has been so great that he flipped and is pushing the yes-no decision off on congress so that if it fails he can blame congress (republicans) and walk away saying it wasn’t his decision. He’s looking for a sure scapegoat.
Telling him he doesn’t need congressional approval and not voting on it pushes the ownership of his disasterous policy back into his lap.
He is answerable to the Constitution and he has no authority in that case to foost us into a war.
He does not own the military. That’s a dictatorial notion