The Senate on Wednesday rejected a Democratic effort to force an end to U.S. military involvement in Iran, voting largely along party lines for the fourth time this year to block a war powers resolution aimed at curbing President Donald Trump’s authority to continue the conflict without congressional approval.

The measure failed 47-52, with Sen. Rand Paul, Republican of Kentucky, joining Democrats in voting for the resolution and Sen. John Fetterman, Democrat of Pennsylvania, opposing it. Sen. Jim Justice, Republican of West Virginia, did not vote. Aside from Justice’s abstention, the vote was identical to the previous war powers vote in the Senate on March 24, despite some Republican lawmakers growing increasingly vocal with their concerns about the war and the timeline to end it.

The resolution would have required the Trump Administration to withdraw U.S. forces from hostilities with Iran unless Congress explicitly authorized the mission. Its defeat marked the latest in a series of unsuccessful attempts by Democrats to reassert Congress’s constitutional authority over decisions of war as the conflict with Iran approaches a crucial two-month mark. 

The War Powers Resolution of 1973, a statute passed in the aftermath of the Vietnam War to limit unilateral military action by the president, requires the executive branch to notify Congress within 48 hours of introducing U.S. forces into hostilities. It also mandates that those forces be withdrawn within 60 days unless Congress declares war or passes an authorization for the use of military force. A single 30-day extension is permitted if the president certifies that additional time is needed to safely withdraw troops.

That 60-day clock is now rapidly running down. The U.S. campaign against Iran began Feb. 28, and the legal deadline based on the Administration’s formal notification to Congress in early March is expected to arrive by May 1. The date has emerged as a pivotal moment for lawmakers, who will soon face a stark choice: approve the war, force its end, or risk allowing the Administration to proceed in defiance of the statute.

"By law, we got to either approve continued operations or stop,” Rep. Don Bacon, a Nebraska Republican, previously told TIME. “If it’s not approved, by law they have to stop their operations.”

So far, Congress has done none of the above. The Senate has now voted four times this year to block resolutions invoking the War Powers Act, effectively allowing the conflict to continue without formal authorization. Republicans have largely argued that cutting off military operations abruptly could endanger U.S. forces and embolden Iran. But Democrats are approaching the May 1 deadline as a moment when Republicans can no longer sidestep questions about Congress’ oversight role over the war.

Sen. Tim Kaine of Virginia, who has spearheaded Democrats’ recent efforts to push War Powers resolutions, told TIME this week that Senate Democrats are preparing to force additional such votes before and after the 60-day deadline.

“Some are suggesting that this is a watershed moment for them and I hope that that's true,” Kaine says of the GOP.

The debate has been sharpened by the Administration’s shifting portrayal of the conflict. Trump initially suggested the campaign would be brief, lasting only weeks, but has since sent mixed signals, at times describing the operation as nearing completion while simultaneously escalating military pressure on Iran.

A White House official said the Administration was in "active conversations with the Hill” on the war powers deadline and added that members of Congress "who try to score political points by usurping the Commander-in-Chief’s authority would only undermine the United States Military abroad, which no elected official should want to do.”