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.
Otherwise, the President is in charge of the armed forces as long as Congress decides to keep paying for them.
Like tin soldiers.........
“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.