Bill Burton, the national press secretary for Obama's campaign, responded to the Republicans' comments.

"The fact that the same Republican candidates who want to keep 160,000 American troops in the middle of a civil war couldn't agree that we should take out Osama bin Ladin if we had him in our sights proves why Americans want to turn the page on the last seven years of Bush-Cheney foreign policy," Burton said.

Iowa has been teeming with activity by Republicans over the past week, both in anticipation of the debate and in preparation for next Saturday's Republican straw poll in Ames, an early test of organizational strength. McCain and Giuliani have pulled out of that contest, but Romney has invested major resources.

Hinting at potential skirmishes in the run-up to the straw poll, Sen. Sam Brownback of Kansas criticized Romney as having shifted his position on abortion as he moved from being governor of Massachusetts to running for president. Brownback's campaign has been calling Iowa Republicans in recent days to remind them that Romney once supported abortion rights.

"There's one word that describes that ad, and it's 'truthful,"' Brownback said in the debate, referring to the calls.

Romney looked sternly toward Brownback and denounced the calls. "I never said I was pro-choice, but my position was effectively pro-choice," he said, referring to the policies he advocated as governor. "I've said that time and time again. I changed my position.

"I get tired of people that are holier than thou because they've been pro-life longer than I have," Romney said.