Senate Majority Leader Harry Reid (D-Nev.) organized the rare all-night session in an attempt to dramatize the fight between Republicans and Democrats over the amendment.

The amendment, which was attached to the Department of Defense authorization bill, had majority support thanks to several Republicans who backed it. But Republicans used a procedural maneuver available to the minority party to require a 60-vote majority to move the bill forward.

Democrats only mustered 52 votes in favor of invoking cloture, falling short of the 60 required. Forty-seven senators voted against cloture. Reid at first voted in favor of cloture, but changed his vote at the last minute to join Republicans opposing it.

Reid’s vote against cloture allows him to call for another vote on the measure at a time of his choosing, according to spokesman Jim Manley, who said the switch was “only for procedure.”

Reid expressed his disappointment at the outcome shortly after the vote but pledged to keep trying to pass legislation aimed at changing course in Iraq.

"We spent two days showing America that we're not going to back down, that we're going to continue to fight," he said. "How could we possibly shrink from this fight? How could we possibly try to avoid this fight?"

Reid had accused Republicans of obstructionism for blocking a simple-majority up-or-down vote on the amendment. But Republicans defended their maneuver as a standard tool of the minority party.

In a news conference before the all night session began Tuesday, Sen. John McCain (R-Ariz.) said that "time after time when the other side was in the minority they also invoked the 60-vote requirement."