If Congress hasn't formally voted to declare war or approve military action against Iran, this resolution would require the President to pull U.S. troops out of any fighting in or against Iran. It's essentially Congress asserting its constitutional authority over decisions to go to war, rather than letting a president continue military action on his own. There's an important exception, though: U.S. forces could still act in self-defense if the United States, or American troops or facilities anywhere in the world, come under attack.