Obama's approval rating, hovering at 50%, is "just enough to get elected" and the president still leads in Ohio, Brownstein noted, but "the idea of any kind of cushion is what is gone."

New ABC News/Washington Post and Politico/George Washington University national polls showed the rise in Romney's favorability ratings, with the Politico-George Washington survey putting him even with the president on that question.

Romney and his campaign have sought to frame the election as a referendum on Obama's presidency, citing high unemployment, slow economic growth from the recession and chronic federal deficits and debt as reasons to deny a second term.

For their part, Obama and Democrats have tried to make the election about competing visions for the future, arguing Republican proposals to repeal major legislation such as health care and Wall Street reforms while expanding tax cuts without identifying additional revenue sources would stall a sluggish but steady recovery.

To Brownstein, Obama needs to spell out how his plans for a second term would be better for the country than what Romney proposes.

"Among the many challenges facing Obama in the next debate, the first among equals is convincing wavering voters that he has a plan to make the next four years better than the last four --something he almost utterly failed to convey at the first debate," Brownstein said.

Galen said those who were quick to criticize the Romney campaign during tough stretches in the primaries and recent months may need to reassess.

"If things turn around and start looking good," he said, "I think you have to give them credit."