Senate Appropriations Chair Susan Collins voted Thursday to introduce a measure to curb the Trump administration’s military operation in Iran, a sign of wavering support among Republican lawmakers as the war is set to reach its 60-day mark at midnight.

Collins’ reversal comes as she is engaged in a tight contest to hold onto her Senate seat in Maine — a race that narrowed earlier Thursday when Democratic Gov. Janet Mills dropped out of the primary race.

Collins and Sen. Rand Paul were the two Republicans who backed the war powers resolution, along with all Democrats except Sen. John Fetterman. The measure fell short of the 51-vote requirement for it to proceed to a vote.

Collins has opposed a number of previous war powers resolutions on Iran since the operation began in February. She told reporters this week that “Congress has to act” if the conflict hits 60 days, which is the limit under the 1973 War Powers Act for a White House to secure congressional authorization.

Collins said in a statement after the vote that she would like to see the Trump administration lay out a plan to withdraw from the region.

“Further military action against Iran must have a clear mission, achievable goals and a defined strategy for bringing the conflict to a close,” Collins said. “I voted to end the continuation of these military hostilities at this time until such a case is made.”

Collins said before the vote that there is an option for the Trump administration to notify Congress of a 30-day extension to its military operation in the region –– a move officials would have to make before the end of the day. But either way, she added, Congress has to intervene.

“As I understand the War Powers Act, the 60 days is the trigger for Congress to act,” Collins said. “There is an additional 30 days, but that is intended for winding down the operations, getting out troops that are in the area. And I think we should follow the law.”

There could be more Republican defections ahead: Sen. Lisa Murkowski of Alaska announced after the vote that if the war passes the 60-day mark without a “credible plan” from the Trump administration, she plans to introduce an Authorization for Use of Military Force for the conflict.

Sen. John Curtis of Utah, who had also indicated the 60-day mark was problematic for him, said in a statement Thursday that he takes the congressional authorization requirement “seriously.”

“I will not support continued funding for the use of force without Congress weighing in,” Curtis wrote. “... As we reach this 60-day mark, it is time for decision-making from both the Administration and from Congress –– and that can happen in league with one another, not in conflict.”

Defense Secretary Pete Hegseth, testifying before the Senate Armed Services Committee on Thursday, said the conflict had not yet reached the 60-day mark because the U.S. and Iran have been engaged in a multi-week ceasefire.

Democratic Sen. Adam Schiff, who introduced Thursday’s resolution, said ahead of the vote that a ceasefire does not stop the clock from ticking. Schiff told reporters that he thinks some Republicans are torn between “the recognition that the Constitution and the law require them to bring this war to an end, and a concern with directly confronting the president.”

“We’ve had more than 200 injured, some very seriously,” Schiff said. “It’s taking a real toll on our economy. Gas prices are now at a new record high. And what’s more, my Republican colleagues, many of them, have acknowledged this date is important to them.”

Collins also voted with Democrats on Tuesday for a different measure to preemptively block military action against Cuba. She had previously voted with a group of five Senate Republicans to introduce a measure in January to curb the Trump administration’s military actions in Venezuela, though that bill also failed in the Senate.