Congressional Democrats are moving in lockstep to block nearly $70 billion in new Iran war funding and back votes demanding Trump pull U.S. troops out.
Just 29% of Americans support the war, and Democrats say Trump has offered no clear strategy, exit plan or persuasive case to Congress after five months of fighting.
House Democrats are even opposing a broader Pentagon policy bill that includes a troop pay raise, using their minority leverage to force Republicans to present an endgame.
Republicans call the stance shameful as munitions concerns grow, but some GOP lawmakers privately and publicly acknowledge the war is unpopular and politically risky ahead of November.
The split marks a historic break from past conflicts such as Iraq and Vietnam, when Democrats often still approved wartime funding despite opposing the wars themselves.