The former president said that Obama's performance showed "how hard he's worked in the last four years to to master that part of the job."

"You could just tell," Clinton continued. "And he did a really good job. He did a good job saying it was time to do nation building here at home and he did a good job explaining that you build the defense budget from the ground up based on the security threats the country faced."

Clinton's comments came a day after the debate, which focused on foreign policy.

A Reuters-Ipsos poll released Tuesday found 47 percent of those surveyed said Obama won the debate, while 31 percent said Mitt Romney won. But the poll also found that, unlike the first debate, the performances were unlikely to change voters' favorability of either candidate.

After the first debate, which Romney is regarded to have won, a number of polls began showing Romney leading Obama. Before that debate, which took place Oct. 3, those same polls showed Obama leading Romney.