WASHINGTON — The Republican-led Congress has missed a crucial window to play a role in the U.S. military operation in Iran, with GOP lawmakers who deferred to President Donald Trump for months on the war now hand-tied by their reticence to challenge him and his administration’s efforts to evade congressional oversight or input.

Since Trump began the war Feb. 28, Republicans have consistently blocked Democratic efforts to halt the hostilities and force the president to win authorization from Congress, arguing that such a move would undermine him in the fight in the Middle East. They have also hung back from putting forth any legislation that would bless the mission and lay out goals, limits and a timeline for withdrawal.

That posture — the latest move by Republicans to cede congressional power to the president — has effectively allowed Trump to run out the clock for quick action by Congress on the conflict.

As their reservations about the war have grown in recent weeks, some Republicans have considered trying to rein in the operation with an authorization that would lay out narrow objectives and criteria for an eventual exit. But they missed a 30-day deadline after the start of the war to force consideration of such a bill.

And the White House this month steered around another statutory milestone of 60 days, which fell on May 1, for Trump to seek permission from Congress to continue the conflict or begin to withdraw forces. His team argued that the 60-day clock had stopped because the ceasefire between the United States and Iran had terminated the conflict, and claimed that the U.S. forces imposing a blockade in the Strait of Hormuz had begun a separate operation called Project Freedom.

That has left critics with fewer tools at their disposal for challenging the military action in the Middle East, and thrust Republicans in Congress into the perilous position of owning an unpopular war during a challenging midterm election year in which they were already in an uphill fight to keep their majorities.

“The Congress does play a very, very direct role,” in matters of war, said Sen. Lisa Murkowski, R-Alaska, who drafted, but never introduced, an authorization that would force the president to develop metrics for success in the fight with Iran and exit criteria. “You can’t do an end run around us.”

But that is exactly what the president did, with help from his party.

In an interview in her office Thursday, Murkowski explained that she had held back on introducing her measure after she could not find enough Republicans willing to join her, and risk the president’s political vengeance. Now that Trump has claimed that the war in Iran is over — an assertion she rejects — she believes there is no current path forward for it in the Senate.

“We have put ourselves in a situation where every bit of that war will be directly attributable” to the president, and a Republican majority that, “in a roundabout way, has allowed for it to happen,” she said.

The 1973 War Powers Resolution, which seeks to limit a president’s ability to wage war without approval by Congress, states that “in the absence of a declaration of war,” the president cannot deploy U.S. combat forces to a foreign nation for longer than 60 days. Legal scholars on both ends of the ideological spectrum reject the idea that a ceasefire pauses that clock. Democrats and a growing number of Republicans have also taken issue with it.

“I don’t know if I really buy that” hostilities have ended, said Rep. Don Bacon, R-Neb., who in recent days signed on to a House bill to authorize the war but force Trump to end the fighting this summer.

The president should not have tried to “do it alone,” Bacon said, comparing Trump’s moves to avoid seeking authorization with a “teenager who comes home late at night” when they knew their curfew all along.

“If you ask me, I think it’s better not to mess around with the law,” he added.

Murkowski said the administration’s claim that the war was over had stymied her efforts to persuade her colleagues to sign on to her authorization measure, giving cover to Republicans who would rather not challenge the president.

“He’s not afraid to use political leverage with anybody, even those on his own red team, and I think you’re seeing that play out,” she said.

Sen. John Curtis, R-Utah, drew a red line at the president waging unilateral war past 60 days, warning in April of “devastation” along the lines of the Vietnam War if clear lines of authority were not established. But on Wednesday, he voted against a war powers resolution that would force Trump to withdraw U.S. troops, saying he was weighing the administration’s claim that the war was over.

“I wouldn’t say I’m totally resolved in my mind,” Curtis said. “But we are in a ceasefire, and I want to see how this thing plays out.”

Democrats have vowed to continue to force votes on war powers resolutions, and three more Republicans broke from their party this week to back such measures. In the House, Reps. Tom Barrett of Michigan and Brian Fitzpatrick of Pennsylvania — both of whom face challenging reelection races — defected Thursday to join Democrats and support moving ahead with such a measure, though it failed on a tie vote.

On Wednesday, Murkowski flipped her position, joining Sen. Susan Collins, R-Maine, who also faces a tough reelection race and switched earlier this month to vote with Democrats, saying she was doing so because the president had passed the 60-day deadline.

Murkowski said she would continue to vote with Democrats on such measures and “oppose any effort to redefine ‘hostilities’ in ways that allow the president to wage war indefinitely without seeking congressional approval as outlined by the Constitution.”

In both chambers, a war authorization faces long odds. By law, such a measure must be introduced within 30 days after the president notifies Congress that U.S. forces are involved in a foreign conflict in order to be fast-tracked to the floor for consideration. With that window now long past, Republican leaders in both chambers, reluctant to anger the president, could leave an authorization bill languishing in committee.

“I don’t think it’s necessary,” Sen. John Thune, R-S.D., the majority leader, said when asked Monday if he would allow a vote on a Republican-led authorization for the war.

“In terms of the, quote, hostilities in the region, there’s been a cessation of that,” he added. “If they should start up again, my assumption is he’ll give us the proper notification.”

If the ceasefire collapses and Trump scales up attacks again, notifying Congress of additional strikes under a new operation, separate from Operation Epic Fury, it could restart the 60-day clock under the 1973 War Powers Resolution. That would give Murkowski, and Barrett, who introduced an authorization bill in the House, another 30 days to try to force a vote.