The Senate blocked a fourth War Powers Resolution (WPR) 47-52 on 15 April. Senator Josh Hawley (Republican of Missouri) told reporters afterwards: "at the end of 60 days, I think we need to vote on a military authorization"1. Hawley added that Donald Trump "does have to come back to Congress" at the 60-day mark and either file a report or seek authorisation.
The WPR 60-day clock, triggered by the 28 February start of hostilities, runs out on Wednesday 29 April, eleven days from this briefing. The House came within one vote of ordering withdrawal on 16 April, failing 213-214. Thomas Massie (R-KY) crossed to support withdrawal and three Democrats who had opposed the 12 April House version, Juan Vargas, Greg Landsman and Henry Cuellar, flipped to support this one. Members of both caucuses have moved in opposite directions on consecutive votes, which means the headline partisan alignment is churning, not hardening.
A Republican senator moving from blocking WPR withdrawals to signalling an authorisation vote opens a third path a Trump-aligned chamber can walk without defecting on headline partisanship. An authorization for use of military force (AUMF) vote on the floor would produce the first signed Iran instrument of the war, under maximally adversarial legislative conditions, and would collapse the verbal-track architecture every prior section of this briefing documents. Roll Call and NOTUS have placed Majority Leader John Thune on the record as working options. The historical comparison is February 2020, when an Iran WPR passed the Senate 55-45 with eight Republican crossovers; Trump vetoed and the override failed. The arithmetic on withdrawal runs closer in 2026, but the two-thirds veto geometry has not moved.
