Updated 5:04 p.m. | The Senate narrowly blocked Sen. Kirsten Gillibrand's bill to remove prosecutorial decisions for military sexual assaults and other felonies from the chain of command.
The measure failed to advance on a 55-45 vote, five short of the 60 votes needed to limit debate. Seventeen of the chamber's 20 women voted aye, while men opposed the measure 42-38.
Senators on both sides of the debate — which has not split along party lines — knew the vote on the New York Democrat's legislation would be close. Gillibrand said earlier Thursday morning that she was "hopeful" her side would have the 60 votes needed to overcome the filibuster hurdle.
"Today too many ... members of the Senate have turned their back on these victims and survivors," of sexual assault, Gillibrand said. "As painful as today's vote is, our struggle on behalf of these brave men and women will go on."
Gillibrand said she thinks her effort will continue to gain momentum going forward, though she noted that a couple of senators who had co-sponsored her measure voted against cloture.
That's a reference to Delaware Democrat Thomas R. Carper and Illinois Republican Mark S. Kirk. Fellow Navy man Sen. John McCain, R-Ariz., could be seen with Kirk in the well of the chamber during the vote, and McCain could be heard saying "Anchors Aweigh," the title of the Naval Academy fight song.
Republicans Mitch McConnell of Kentucky and Michael B. Enzi of Wyoming apparently hadn't publicly committed, but voted with Gillibrand .
Sen. Lindsey Graham, R-S.C., who has vast experience as a military lawyer, said a vote in favor of the Gillibrand proposal could come back to haunt to GOP presidential aspirants in the Senate.
"People wanting to run for president on our side, I will remind you of this vote. You want to be commander in chief? You told me a a lot today about who you are as commander in chief," Graham said. "You were willing to fire every commander in the military for reasons I don't quite understand. So we will have a good conversation as to whether or not you understand how the military actually works."
Sens. Rand Paul, R-Ky., and Ted Cruz, R-Texas, are among the possible 2016 contenders who expressed vocal support for Gillibrand's plan.
Shortly before the voting started, Gillibrand rejected the idea that the trust many senators have for superior officers in the armed forces is relevant if victims of sexual abuse do not share that trust and therefore do not report attacks.
Gillibrand supporter Sen. Barbara Boxer expressed a similar sentiment.
"I know that Sen. McCaskill is trying to fix these problems around the edges. Fine, but let's get to the heart of the matter," the California Democrat said. "We can continue the 20 years of baloney and not make the change that needs to be made."
New Hampshire Republican Kelly Ayotte has led the effort against Gillibrand's plan, along with pushing an alternate proposal with Missouri Democrat Claire McCaskill.
Ahead of the vote, Ayotte said the onus was on Gillibrand to get 60 votes, but she was "optimistic" the Senate would reject it. Gillibrand had 55 senators expressing public support leading up to the vote, including recently appointed Montana Democrat John Walsh.
Majority Whip Richard J. Durbin, the chairman of the Appropriations Subcommittee on Defense, is among the supporters of Gillibrand's proposal. Durbin said Thursday morning he had not whipped the measure, however.
Armed Services Chairman Carl Levin has been outspoken in support of the proposal offered by McCaskill and Ayotte and is staunchly against the Gillibrand measure.
"These additional protections in the McCaskill-Ayotte bill help us answer the key question: How can we best strengthen our protections against military sexual assault? We do so by empowering victims and by holding our commanders accountable. But we threaten to weaken those protections if we undermine the authority of the very commanders who must be at the heart of the solution," the Michigan Democrat said. "Powerful evidence should lead us to the conclusion that we should not remove the authority of commanders to prosecute these cases."
"More than anything, the victims of sexual assaults, the survivors, need to have the confidence that the legal system in which they reported crime will produce a just and fair result. We need to encourage more reporting, and that is what Sen. Gillibrand's bill will accomplish," Republican Susan Collins of Maine said.
McCaskill and Ayotte outlined the findings of the Response Systems Panel, which rejected the idea of removing the convening authority in alleged sexual-assault cases from the chain of command. They also noted changes already made with the fiscal 2014 defense authorization law.
"It is clear that right now we have more cases going to court-martial over the objections of prosecutors than the objections of commanders," McCaskill said during floor debate. "Today there is a court-martial ongoing where a prosecutor walked away from the serious charges and the commander said go forward."
The legislation from McCaskill, Ayotte and Nebraska Republican Deb Fischer flew over the cloture hurdle, securing all 100 votes, but it will be held over for final passage until Monday due to what Ayotte described as a misunderstanding.
McCaskill, Ayotte and Fischer were the only three women in the Senate to oppose the Gillibrand measure.
Humberto Sanchez contributed to this report.