Senate Advances Bill to End Iran War as Cassidy Flips Vote

The U.S. Senate voted 50-47 on Tuesday to advance a War Powers Resolution that would compel President Donald Trump to withdraw American forces from hostilities in Iran, marking the first time the chamber has moved forward on such a measure after seven failed attempts. The breakthrough came when Sen. Bill Cassidy (R-LA) flipped his vote to support the resolution just days after losing his GOP primary to a Trump-endorsed challenger.

A Crack in the Republican Wall

For months, Senate Republicans had successfully blocked every Democratic-led effort to force a debate on the legality and scope of the Iran war. But Tuesday’s procedural vote to discharge the resolution from the Senate Foreign Relations Committee revealed a growing unease within the Republican conference over a conflict that has stretched into its third month with no clear end in sight.

According to AP News, the resolution — introduced by Sen. Tim Kaine (D-VA) — would direct the president to “remove the United States Armed Forces from hostilities within or against Iran, unless explicitly authorized by a declaration of war or a specific authorization for use of military force.” Joining Cassidy in supporting the measure were Sens. Rand Paul (R-KY), Lisa Murkowski (R-AK), and Susan Collins (R-ME), all of whom had voted yes on previous attempts.

Sen. John Fetterman (D-PA) was the only Democrat to vote against the resolution, as he has on every previous occasion, NBC News reported.

Cassidy’s Political Calculus

Cassidy’s decision to break with the White House came after a decisive primary defeat on May 16, when he finished third behind Trump-endorsed Rep. Julia Letlow and Louisiana Treasurer John Fleming. The loss ended his Senate career and appeared to free him from the political pressure that had kept him in line with the administration on seven prior war powers votes.

“While I support the administration’s efforts to dismantle Iran’s nuclear program, the White House and Pentagon have left Congress in the dark on Operation Epic Fury,” Cassidy said in a statement. “In Louisiana, I’ve heard from people, including President Trump’s supporters, who are concerned about this war. Until the administration provides clarity, no congressional authorization or extension can be justified.”

Cassidy had been a target of Trump’s since voting to convict the president in his second impeachment trial following the January 6, 2021, Capitol attack. Trump actively campaigned against him, and his loss was widely seen as a demonstration of the president’s continued grip on the Republican Party.

Growing Bipartisan Momentum

Senate Minority Leader Chuck Schumer (D-NY) celebrated the vote as evidence of shifting political dynamics. “Republicans are starting to crack, and momentum is building to check him,” Schumer said in a statement after the vote, as reported by AP News. “We are not letting up.”

The progression of Republican defections has been gradual but steady. Early votes saw only Rand Paul crossing party lines. On May 13, Murkowski flipped her vote. Now Cassidy’s defection brings the total to four Republican supporters — still short of the number needed to guarantee final passage.

Three Republican senators were absent for Tuesday’s vote: John Cornyn (R-TX), Thom Tillis (R-NC), and Tommy Tuberville (R-AL). If all three return and vote against the resolution, the final passage vote could end in a 50-50 tie, which would be broken by Vice President JD Vance, almost certainly against the measure.

Steep Hurdles Ahead

While Tuesday’s vote was a significant political milestone, the resolution faces formidable obstacles before it could become law. The House is expected to vote on a similar war powers resolution on Wednesday, but the Republican-controlled chamber has already blocked three previous attempts, with one ending in a tie.

Even if both chambers pass the legislation, Trump is expected to veto it. Overriding a veto would require two-thirds majorities in both the House and Senate — a very high bar given the current political alignment.

The White House has also constructed a legal argument to circumvent the War Powers Resolution of 1973, which limits presidential war-making to 60 days without congressional authorization. The administration claims that the ceasefire declared on May 1 “terminated” hostilities with Iran, effectively resetting the clock. Despite this assertion, U.S. troops continue to blockade Iranian ports, and Iran maintains its blockade of the Strait of Hormuz, as Al Jazeera reported.

Economic Pressures Drive Debate

The political calculus around the war is increasingly shaped by its economic impact. Sen. Chris Murphy (D-CT) highlighted the domestic toll in a floor speech, noting that “peace negotiations are stuck and so day after day after day grocery prices climb, gas prices climb.” Rising costs have fueled public opposition to the conflict, which in turn has pressured Republican lawmakers to reconsider their positions.

Sen. Mike Rounds (R-SD), who voted against the resolution, acknowledged the growing concern among his colleagues. “The War Powers Resolution of 1973 does provide an avenue for that discussion and debate to occur,” Rounds told AP News. “But I think a number of our members maybe just feel like it’s time to have the debate.”

What to Watch

The coming days will determine whether the Senate can secure the votes for final passage. The return of the three absent Republicans will be critical, as will the outcome of the House vote. Meanwhile, Trump’s decision on Tuesday to endorse Sen. Cornyn’s primary opponent in Texas signals that the president is intensifying his purge of Republicans who cross him — a dynamic that could either deter further defections or, as in Cassidy’s case, free lame-duck senators to vote their conscience.

For now, the vote represents the most significant congressional challenge yet to presidential war powers since the conflict began, and a clear signal that patience on Capitol Hill is wearing thin.