The United States Senate has cleared a key procedural hurdle on a War Powers Resolution that would require President Donald Trump to either obtain congressional authorisation for the ongoing conflict with Iran or withdraw American forces. The vote, passed 50 to 47 on Tuesday, marks the first time such a measure has advanced past this stage after seven previous failed attempts — a rare and significant rebuke of a sitting president by members of his own party.

The breakthrough came in part because of a notable political defection. Republican Senator Bill Cassidy of Louisiana, who recently lost his primary election to a Trump-endorsed challenger, crossed the aisle to provide a crucial vote in favour of the resolution. He was joined by fellow Republicans Rand Paul, Susan Collins, and Lisa Murkowski, along with nearly all Democratic senators. The sole Democrat to vote against the measure was Pennsylvania Senator John Fetterman. Three Republicans were absent from the chamber entirely — absences that could prove decisive in any future vote.

Senate Democratic Minority Leader Chuck Schumer framed the vote in stark terms ahead of the tally.