The verbal jousting took place across Virginia, where both wooed voters in one of the battleground states that will determine the outcome of the November 6 election.

With 40 days to go and polls showing an narrowing path to victory for the Republican nominee, Romney warned a second Obama term would be subsumed by economic malaise as he tried to draw the battle away from his own perceived missteps and back to the president's economic record.

Romney pounced on data showing the US economy was more sluggish than thought in the second quarter, growing only 1.3% instead of the prior estimate of 1.7%.

"The Obama economy is officially stuck in neutral," Romney's campaign warned.

Second-quarter gross domestic product marked the slowest growth since the first quarter of 2011, and followed a 2.0% annual pace in the first quarter.

"This is a real challenge for us, and this is not just one quarter," Romney told a few hundred military veterans in Springfield, just outside the US capital, as he harangued Obama over the stuttering economy.

"China's growing much faster than we. Russia's growing faster than we. Our economy needs to be reinvigorated."

Obama agreed, but said adhering to Romney's vision, which includes a 20% tax cut across the board, would not help Americans get there.

"He thinks that if you just spend another $5 trillion on tax cuts that favor the wealthiest Americans, if you get rid of more regulations on Wall Street, and jobs and prosperity will rain down on everyone. The deficit will magically disappear," Obama told a crowd in Virginia Beach.

But "top-down economics doesn't work," he said. "We don't need to double down on the same trickle-down policies that got us into this mess in the first place."

Obama again slammed Romney for his recently unearthed comments that "47%" of Americans will vote for Obama because they are government-dependent freeloaders.

"I don't think we can get very far with leaders who write off half the nation as a bunch of victims who never take responsibility for their own lives," Obama said.

The Virginia duel marks the third straight day Obama and Romney are cat-and-mouse campaigning in the same state.

Meanwhile, early or absentee voting has begun in more than half of the 50 states, including Iowa, where early voting stations opened on Thursday.

Iowa is one of five battleground states, including Ohio and Virginia, that analyst Larry Sabato moved from the "toss-up" column to "leans Democratic."

It marks a potentially devastating setback for Romney, as the changes would send Obama beyond the 270 out of 538 electoral college votes needed to win the White House.

But Sabato, a University of Virginia professor, insisted Romney could thrust himself back into contention if he bests Obama in the three debates, beginning October 3 in Colorado.

"If Romney fares particularly well or Obama does poorly, the drift of this contest could change," Sabato wrote on his popular political website.

Romney's fading numbers appeared to reflect damage from the release last week of the secretly filmed "47%" video.

The former Massachusetts governor softened his tone Wednesday, saying his "heart aches" for people struggling to find work and the government "has a role" in taking care of people who are hurting.

He also released a TV ad where he looks into the camera and says: "President Obama and I both care about poor and middle class families. The difference is, my policies will make things better for them."

Obama countered on Thursday with a two-minute, direct-to-camera ad of his own, in which he called for "a new economic patriotism" focusing on job creation, expanded US energy, improved education and balancing the budget.

He fleshed out the theme in Virginia.

"I travel around the world and I know there's not another country on Earth that wouldn't trade places with the United States of America," Obama boasted.

As both men stumped on Wednesday in Ohio, Romney insisted "we're going to win," despite a Quinnipiac University/New York Times/CBS News poll showing him down 10 points in the key Midwestern state, which no Republican has ever lost and still won the White House.

The poll also showed Romney down nine points in the major battleground state of Florida, completing a scenario that would deny him a credible path to victory.