“Why hasn't Congress done it's job on the war?”
The only question really worthy of an answer. The “what ifs” have no pat answer.
As to the above, Congress hasn’t done its Constitutional duty on any of our wars since 1941. They would rather shirk the responsibility so each party can lay the blame for the results on the other. They have determined that “resolutions” are good enough, no one wants to actually declare war anymore. With a resolution the buck can be passed upstairs.