“If he wants to command them against a sovereign state recognized by the US as legitimate, then Congress has to declare a state of war.”
Here’s my understanding. The president can engage any country for 90 days. By that time Congress must either declare war or back the president. If they don’t he has to stop.
Having said that, I don’t think there’s any mechanism to force the president to stop. Our system worked because all sides obeyed the law and the Constitution. If the president continues and the Senate will not convict on impeachment then I see no way to stop Obama.
I think what you mean is that Congress must either declare war or vote to stop funding or continue funding the war.
The Democrats certainly did not back Bush regarding Iraq, but they also did not vote to defund the Iraq operation.