WASHINGTON — The Senate on Thursday rejected a controversial bipartisan bill to remove military commanders from decisions over the prosecution of sexual assault cases in the armed forces, delivering a defeat to advocacy groups who argued that wholesale changes are necessary to combat an epidemic of rapes and sexual assaults in the military.
The measure, pushed by Senator Kirsten E. Gillibrand, Democrat of New York, received 55 votes — five short of the 60 votes needed for advancement to a floor vote — after Gillibrand’s fellow Democrat, Senator Claire McCaskill of Missouri, led the charge to block its advancement.
The vote came after a debate on the Senate floor filled with drama and accusations that Gillibrand and her allies were misguided.
“What Senator Gillibrand is doing is way off-base,” Senator Lindsey Graham, Republican of South Carolina, said, his voice rising.
“It will not get us to the promised land of having fewer sexual assaults.”
The debate pitted the Senate’s 20 women against one another and seemed bound to leave hard feelings, given that a solid majority of the Senate actually backed Gillibrand’s proposal.
“The only reason some are forcing a filibuster on the Gillibrand vote is because they know we have a majority,” said Senator Barbara Boxer, Democrat of California, who supported the bill, pointing to a sign that said “Don’t Filibuster Justice.”
But McCaskill would not budge and refused to allow the Gillibrand bill to get a yes-or-no vote.
Several Republicans, including Senator Rand Paul of Kentucky and Senator Charles Grassley of Iowa, supported the Gillibrand proposal and expressed deep frustration with the military’s failure to stem the number of sexual assaults.
Congress began scrutinizing the sexual assault problem in the military after a recent series of highly publicized cases, including one at the Naval Academy, and after the release of new data from the Pentagon on the issue.
On Sept. 30, the end of the last fiscal year, about 1,600 sexual assault cases in the military were either awaiting action from commanders or the completion of a criminal investigation.
Critics of the military’s handling of such cases say the official numbers represent a tiny percentage of sexual assault cases, while Gillibrand said that only 1 in 10 sexual assault cases were reported.
She and her supporters argue that forcing sexual assault victims to go to their commanders to report cases is similar to forcing a woman to tell her father that her brother has sexually assaulted her.
Because commanders often know both the victims and the alleged abusers, Gillibrand’s supporters say, victims often shy away from reporting abuse.
Military commanders, they say, have not proven themselves able to deal with the issue.
“The definition of insanity is doing the same thing over and over again and expecting a different result,” Paul said.
Grassley added: “The Defense Department has been promising the American people for a long time that they’re working on the problem of sexual assault.”
Then he said, “Enough is enough.”
Three months ago, Congress passed legislation preventing commanders from overturning sexual assault verdicts. The measure also expanded a victims counsel program for the survivors of sexual assault throughout the military and made retaliation for reporting assault a crime.
After blocking Gillibrand’s bill, the Senate agreed, 100 to 0, to move ahead with a measure sponsored by McCaskill and two Republicans, Senators Kelly Ayotte of New Hampshire and Debra Fischer of Nebraska.
The legislation calls for a civilian review if a prosecutor and commander disagree over whether to litigate a sexual assault case.
A vote on that bill is scheduled for next week.
After Thursday’s vote, Gillibrand said she will continue her efforts on behalf of victims of sexual assault in the military.
Paul Rieckhoff, the founder and executive director of Iraq and Afghanistan Veterans of America, called Thursday’s vote part of “a frustrating pattern.”
The Senate, Rieckhoff said, “has chosen to keep the status quo. Our lawmakers should be able to provide a fair and effective military justice system worthy of our veterans and service members.”