The Republican-majority US House of Representatives has passed a resolution to force President Donald Trump to seek Congressional approval for the Iran war or withdraw US forces — a major rebuke to his military campaign.At the heart of the vote on Wednesday (June 3) is the longstanding dispute over the division of war-making powers between the President and the US Congress — comprising the House of Representatives (the lower house) and the Senate (the upper house). That debate is shaped by the War Powers Resolution of 1973, a law intended to limit a President’s ability to conduct prolonged military operations without Congressional authorisation.Despite the 215-208 resolution in the House, with four Republicans siding with Democrats, the vote will remain symbolic unless it is cleared in the Republican-dominated Senate. Even then, the question of whether War Powers Resolutions are constitutional remains a subject of debate.Under the 1973 War Powers Resolution, Presidents who deploy US forces in conflicts without Congressional authorisation must notify Congress within 48 hours and end the operation after 60 days, unless Congress votes for continued deployment. The law also grants the president an additional 30 days to safely withdraw troops, not to extend combat.Since Trump formally notified Congress of the military action against Iran on March 2, the statutory end date was May 1.The law is automatically invoked, without Congress having to pass a resolution to implement it or vote on the subject.Also in Explained | Trump tells Congress hostilities in Iran have ‘terminated’. Does War Powers Act still apply?While Congress has neither declared war nor authorised the conflict, Republicans have blocked several Democratic Party-led efforts to limit Trump’s ability to act without Congressional approval or bring the war to an end.Story continues below this adSo why did the House vote if the War Powers Resolution is already law?The answer lies in decades of disagreement between Congress and the White House over how the law should be applied.In a 1999 Congressional Research Service report, analyst Richard F Grimmett wrote that “the heart of the challenge” to the War Powers Resolution’s constitutionality rests on “differing interpretations” of the respective war powers of Congress and the president.Successive administrations across the Democratic and Republican parties have questioned whether certain military operations fall within the scope of the War Powers Resolution, arguing that the president retains broad constitutional authority as commander-in-chief to deploy US forces without prior Congressional approval.Story continues below this adAs a result, Congress has repeatedly turned to war powers resolutions to formally assert its authority over military action and to direct Presidents to end unauthorised hostilities.What happens when the resolution reaches the Senate?The resolution now faces its biggest test in the Senate before it can advance further. Given that the Republican-controlled Senate, whose members have largely backed Trump throughout the conflict, has not yet passed a war powers resolution aimed at limiting the President’s authority, its prospects remain uncertain.The Senate advanced a separate but similar war powers resolution last month, although further votes on the measure have not yet been scheduled. According to a Reuters report, seven previous attempts to advance a similar measure in the Senate had failed.NewsletterFollow our daily newsletter so you never miss anything important. On Wednesday, we answer readers' questions.SubscribeEven if the Senate approves the measure, its practical effect remains unclear. While war powers resolutions can be used to express Congress’s position without Presidential approval, courts have long debated whether lawmakers can compel a president to withdraw troops through such a mechanism. That uncertainty stems in part from a 1983 Supreme Court ruling that struck down legislative vetoes, forcing Congress to rethink how it enforces the War Powers Resolution.Story continues below this adThere is also the broader constitutional question. In a 1993 legal assessment, the Justice Department’s Office of Legal Counsel argued that Congress “could not, by mere legislation, deprive the President” of constitutional authority implied by the commander-in-chief role. Successive administrations have similarly argued that Congress cannot unduly restrict the President’s authority as commander-in-chief, raising the prospect of a legal challenge should lawmakers seek to compel an end to military operations.This is also why the Republican defections were significant. While four votes are unlikely to alter the resolution’s immediate prospects, they suggest some erosion in support for the conflict within Trump’s own party in the run-up to the midterm Congressional elections.According to The New York Times, Republican leaders had postponed an earlier vote on the measure after concluding they lacked the numbers to defeat it, only for the resolution to pass when it finally came to the floor. Should that sentiment spread, Senate Republicans could face growing pressure to break with the White House on future votes related to the war.