More than a half hour later, Obama returned to the subject, saying that Romney had once said it wasn't worth moving heaven and earth to catch one man, a reference to the mastermind behind the 9/11 terror attacks.
"You said we should ask Pakistan for permission," Obama said. "And if we had asked Pakistan permission, we would not have gotten him. And it was worth moving heaven and earth to get him."
The president said he had ended the war in Iraq, was on a path to end the U.S. combat role in Afghanistan and has vowed to bring justice to the Benghazi attackers.
He also jabbed at Romney's having said during the campaign that Russia is the United States' No. 1 geopolitical foe.
"Governor, when it comes to our foreign policy you seem to want the policies of the 1980s, just like you want to import the social policies of the 1950s and the economic policies in the 1920s," Obama said.
Obama took a mocking tone after Romney, criticizing the administration's Pentagon budget, said disapprovingly the U.S. Navy has fewer ships than at any time since the end of World War I.
"I think Governor Romney maybe hasn't spent enough time looking at how our military works. You mentioned the Navy, for example, that we have fewer ships than we did in 1916. Well, Governor, we also have fewer horses and bayonets because the nature of our military has changed. We have these things called aircraft carriers where planes land on them."
The televised debate brought no cessation to other campaigning.
Obama's campaign launched a television ad in Florida that said the president ended the war in Iraq and has a plan to do the same in Afghanistan, accusing Romney of opposing him on both. It was not clear how often the ad would air, given the fall's overall focus on the economy.
Vice President Joe Biden, campaigning in Canton, Ohio, emphasized differences between the two candidates on the war in Afghanistan.
"We will leave Afghanistan in 2014, period. They say it depends," he said. "Ladies and gentlemen, like everything with them, it depends. It depends on what day you find these guys."
Romney's running mate, Wisconsin Rep. Paul Ryan, was in Colorado. "We are in the midst of deciding the kind of country we're going to be, the kind of people we're going to be, for a generation," he said.
Whatever the outcome of the final face-to-face confrontation, the debates have left an imprint on the race. Romney was widely judged the winner of the first debate over a listless president on Oct. 3, and he has risen in polls in the days since. Obama was much more energetic in the second.
Monday night marked the third time in less than a week that the president and his challenger shared a stage, following the feisty 90-minute town-hall-style meeting last Tuesday on Long Island and a white-tie charity dinner two night later where gracious compliments flowed and barbs dipped in humor flew.
Espo reported from Washington.
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