Last month polls in Michigan indicated the president with a healthy lead but an EPIC-MRA survey released Monday showed his advantage had slipped to 48 percent-45 percent.

And new polls in New Hampshire and Pennsylvania, where Obama held leads last month, now suggest much closer contests.

With this week's vice presidential debate and two more showdowns between Obama and Romney still to come, the polls can quickly shift again. But the new numbers this week suggest the race has changed.

"The new polls don't mean Romney is going to win, or is even ahead today if it was possible to precisely measure that. But they do mean that we are returning to a race that reflects the country's near 50-50 division over Obama's performance and, as such, is likely to remain close and within reach for both men through November," Brownstein said.