WASHINGTON -- Sen. Kirsten Gillibrand lashed out at the Pentagon and the president Tuesday after her controversial measure on prosecuting military sexual assault won a Senate majority but fell short of the 60 votes needed to pass.

The junior Democratic senator from New York attacked the "Pentagon spin machine" for obscuring its lack of progress on curbing assaults and President Barack Obama for not addressing the issue after promising in 2013 that he would.

"We are not going away," Gillibrand said in a news conference with some of her bipartisan co-sponsors after the measure failed 50-49. "The vote is over but we are going back to our office to get ready for the next one."

Gillibrand makes new push on military sex assault billGillibrand bill on military sex assaults fails

Gillibrand's measure would fundamentally change how the U.S. military addresses sexual assault cases, shifting authority from commanders to attorneys to prosecute those crimes.

In December 2013, Obama gave the military a year to fix its handling of sexual assaults.

"If I do not see the kind of progress I expect, then we will consider additional reforms," he said then. But Gillibrand said Obama hasn't raised the issue again. "I expected more of him than that," she said.

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Tuesday morning, before the vote, she engaged in a debate over her Military Justice Improvement Act with opponents Sen. Claire McCaskill (D-Mo.) and Sen. John McCain (R-Ariz.).

McCaskill said surveys show military sexual assaults dropped 29 percent in the past two years and reporting of incidents rose from 1 in 10 victims to 1 in 4.

"I must urge this body to reject the Gillibrand approach, which removes commanders from being held accountable where they must be held accountable," McCaskill said.

"That couldn't be farther from the truth," Gillibrand retorted. "Today, commanders are the only ones responsible for good order and discipline. . . . They have failed in that duty."

She said surveys show the commanders have not stopped retaliation: 62 percent of victims said they faced it when they reported assaults.

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Tuesday's vote was the second time Gillibrand's measure won a majority but fell short of the 60-vote threshold. In March 2014, the Senate voted 55-45 to end a filibuster of her bill.

Gillibrand said 10 senators who voted with her last year are no longer in Congress, but she picked up five new votes.