The Senate on Thursday rejected a Democratic-led effort to force the removal of U.S. forces from Iran, turning back a War Powers Resolution just one day before a critical legal deadline that even some Republicans acknowledge amounts to a binding constraint on President Donald Trump’s authority.

The procedural measure failed 47 to 50, with Sens. Susan Collins of Maine and Rand Paul of Kentucky the only Republicans breaking with their party as Congress again declined to assert its authority over a war that has entered its eighth week without formal approval. Significantly, it was the first time Collins had voted for such a measure, making her the first Republican to do so since the war began in late February. Sen. John Fetterman of Pennsylvania continued to be the lone Democrat voting against the resolution.

The vote came on the eve of a May 1 deadline that carries unusual legal weight under the War Powers Resolution of 1973, a statute enacted in the aftermath of the Vietnam War to restrain unilateral presidential military action. Under the law, a president who “introduces U.S. forces into hostilities” must terminate those operations within 60 days unless Congress declares war or passes an authorization for the use of military force. The statute allows for a single 30-day extension, but only if the president certifies that additional time is necessary to ensure the safe withdrawal of troops.

The Trump Administration formally notified Congress of its military campaign on March 2, triggering the clock that expires Friday. Absent congressional authorization or a withdrawal certification, many legal scholars and lawmakers argue that the U.S. will be violating federal law if it continues military action in Iran after Friday. 

“The President’s authority as Commander-in-Chief is not without limits,” Collins said in a statement after she voted for the measure. “The Constitution gives Congress an essential role in decisions of war and peace, and the War Powers Act establishes a clear 60-day deadline for Congress to either authorize or end U.S. involvement in foreign hostilities. That deadline is not a suggestion; it is a requirement.”

Collins added that additional military action against Iran “must have a clear mission, achievable goals, and a defined strategy for bringing the conflict to a close” and that she voted to end the continuation of the war “until such a case is made.”

Yet the Senate’s vote highlighted how reluctant lawmakers remain to take that step. For two months, Democrats have forced a series of votes aimed at compelling the Administration to either wind down the conflict or seek authorization. All six resolutions have failed, revealing the limits of congressional appetite—particularly among Republicans—to directly challenge a President of their own party, particularly on matters of war.

At the same time, the approaching deadline has begun to shift the conversation on Capitol Hill. Several Republicans who opposed the Democratic resolution, including Collins, had previously told TIME they nonetheless view the 60-day mark as legally significant and had been expecting the administration to engage Congress about next steps.

“It’s the law,” Sen. James Lankford of Oklahoma told TIME in mid-April of the requirement to authorize continued operations. Sen. Thom Tillis of North Carolina suggested that if the United States plans to remain engaged in Iran beyond the immediate term, Congress should pass a formal authorization. “It all depends on the information that gets conveyed to us about the strategic objectives, the timing, all that stuff needs to come before us,” he told TIME.

Still, those concerns have not translated into support for a War Powers Resolution brought by Democrats, which many Republicans dismiss as overly political or insufficiently tailored to military realities. Some have floated alternatives, including narrower authorizations or limits on ground troops, while others have suggested the administration could invoke the law’s 30-day withdrawal provision to buy more time.

Trump Administration officials have signaled it may not accept the premise that the statute strictly applies, noting that combat operations have fluctuated in recent weeks and emphasizing that lawmakers have been kept informed through briefings. During a Senate hearing on Thursday, Defense Secretary Pete Hegseth told lawmakers that the Administration’s interpretation of the War Powers Resolution is that the “60day clock pauses or stops in a ceasefire.”

“We are in a cease fire right now, which our understanding means the 60-day clock pauses or stops in a cease fire,” Hegseth said. “It's our understanding.”

“I do not believe the statute would support that,” Democratic Sen. Tim Kaine of Virginia responded. “The 60 days runs…tomorrow, and it's going to pose a really important legal question for the Administration there. We have serious constitutional concerns, and we don't want to layer those with additional statutory concerns.”

Democrats, increasingly frustrated after repeated legislative defeats, are now exploring more aggressive options. TIME reported this week that some lawmakers are privately discussing whether to sue the President if military operations continue beyond the deadline without authorization, setting up a potential constitutional clash over the separation of powers.

“Legal action has to be explored,” Sen. Richard Blumenthal of Connecticut told TIME, reflecting a broader debate within the party about how to compel compliance with a law that has historically proven difficult to enforce.

Others caution that the courts may offer little relief. Federal judges have often declined to intervene in disputes over war powers, deeming them political questions or ruling that lawmakers lack standing to sue. Even so, some Democrats argue that allowing the deadline to pass without consequence would effectively render the statute meaningless.

“If we don't have standing,” Rep. Ted Lieu of California told TIME, “then it would mean that, basically, this law could never be enforced.”

Even as some in the party weigh legal action, Democratic leaders say they are focused on exhausting legislative avenues, including additional War Powers votes and potential efforts to restrict funding for the conflict. That role—enshrined in Article I of the Constitution—gives Congress the authority to declare war, a power the War Powers Resolution sought to reinforce after decades of expanding executive action.

Yet more than 50 years after its passage, the law has never successfully forced a president to end a military operation. Presidents of both parties have often sidestepped its requirements, while Congress has struggled to muster the unity or political will to compel compliance.