The US Senate has decided not to debate a resolution criticising President George W Bush's troop surge in Iraq.
The first of the 21,500 extra troops are already in Baghdad
The rare Saturday session followed a non-binding vote backing the resolution in the House of Representatives.
In the House, 17 Republicans had joined the majority Democrats to oppose the increase of 21,500 troops.
Democrats needed the support of 60 of the 100 senators to advance the same motion in the Senate, but they only managed to gain 56 votes in favour.
Mr Bush still faces battles with Congress over funding for US troops in Iraq.
Although both the Congressional resolutions are non-binding, the president needs the legislators to support his $93bn (£48bn) emergency troop-funding measure.
The White House has dismissed the vote, and warned Congress against trying to cut off funding.
Under Mr Bush's new Iraq strategy, 21,500 extra troops are being sent, mostly to the capital Baghdad, to help enforce new security measures.
'More war or less war'
Senate Democrats were hoping to repeat their Friday success in the House, when the motion criticising the president's Iraq policy was passed by 246 votes to 182.
"Today's vote is an opportunity to send a powerful message," said Democratic majority leader, Senator Harry Reid, during an emotional discussion.
"The Senate's responsibility must be to vote on escalation, whether the so-called surge is supported or opposed. This is the choice. More war, or less war," the Democratic leader told the Senate.
Republicans sought debate on a different motion, which would have ruled out any budget cuts affecting troops already in Iraq.
"A vote in support of the troops that is silent on the question of funds is an attempt to have it both ways," said Senator Mitch McConnell, the Republican leader.
Only seven Republicans broke ranks with the party, and so the Democrats failed to reach the 60 votes needed to pass the motion.
The House vote on Friday in support of the non-binding motion brought to a close the first full debate there since the Democrats took control of Congress in January.
Speaking after the vote, House of Representatives Speaker Nancy Pelosi said it would send an unmistakable signal to the White House.
"The bipartisan resolution today may be non-binding. But it will send a strong message to the president - we here in Congress are committed to protecting and supporting our troops."
House Minority Leader John Boehner had urged lawmakers to vote against the motion, saying it was "the first step towards a tragic, unthinkable goal".