The senate blocked an effort to repeal the law banning gays from serving openly in the military.
Republicans balked when democrats tried to push the bill through.
The senate has voted against repealing don't ask don't tell in the military.
Democrats were counting on republican Senator Susan Collins to cast the decisive 60th vote for the bill, but the senator from Maine changed her mind at the last minute.
She says, "I think we should welcome the service of these individuals, but I cannot vote to proceed to this bill under a situation that is going to shut down the debate and preclude republican amendments. That too is not fair. "
Even democratic strategists call the vote a train wreck. If the democrats lose seats in congress in the midterm elections, it could be even harder for President Obama to get rid of the ban on gays down the road.
The newly appointed head of the marines told a senate panel, repealing Don’t Ask Don't Tell during wartime would be a distraction.
Democratic Senator Roland Burris, Illinois, said "You do not support the statute change - is that correct?”
Amos says, "Senator Burriss, I do not. I don't know yet what the impact on recruiting and retention will be and our combat readiness."
Defense secretary Robert Gates asked congress to wait on the vote until the military finished its study on the issue. Many top republicans, including former POW John McCain echoed that sentiment.
The pentagon report is due in December.
Alabama senators, Jeff Sessions and Richard Shelby both voted against the measure.