The first head-to-head debates of the race have shaken up the campaign arithmetic, and given Romney and vice-presidential running mate Paul Ryan momentum as they roll into the last weeks before November 6.
Until Obama's lacklustre first debate last week, the Democrat looked to be on course for victory, with a narrow lead over the Republican in national polls and a lock on the key swing states that will decide the result.
But Romney triumphed in the head-to-head, and Ryan made no major errors in his debut Thursday against Vice President Joe Biden, leaving the Republicans slightly ahead nationally and making inroads in battleground districts.
An average of polls conducted by the respected website RealClearPolitics gave Romney a one point lead nationwide, and showed him winning in swing states Florida, North Carolina and Colorado – also targets for Obama.
But Obama retains narrow leads in Ohio, Virginia and Iowa, and most pundits, bookmakers and online prediction markets still expect the incumbent to win a second term with a majority of votes in the electoral college.
Biden's aggressive debating turn enthused Obama's Democratic supporters, but pundits expressed doubt that it would convert many waverers, and the younger and less experienced Ryan was seen as having held his own in the key test.
Now all eyes are turning back to the top of the ticket. A good debate performance from Obama on Tuesday could smother memories of his disastrous first outing – or Romney could set the seal on his newfound narrow lead.
This new reality was underlined by the rivals' choice of Friday schedules. Romney remained on the trail with flying visits to swing states Virginia and Ohio, but Obama was hunkered down practicing his lines for Tuesday.
The tedious work was not interrupted by reports that a shot was fired Friday at a campaign office for President Obama in the state of Colorado, shattering a window but injuring no one.
A photo posted online showed a window broken at the front of the office. Police said they were searching for a "possible vehicle of interest."
Meanwhile, having shown his boss how to debate, Biden tried to crank up the energy of his performance in a trip to Wisconsin, Ryan's home state, and a battleground Obama badly needs in his column on November 6.
He lashed out at Romney over the content of secretly filmed tape in which the Republican nominee branded 47% of Americans as "victims" who were dependent on the government and paid little in tax.
"Folks, it's about time Governor Romney take some responsibility to help the American people, the middle class," Biden told 2 000 people in La Crosse.
Romney was campaigning alongside Ryan, hoping some of the glory from his running mate's debate performance would rub off as they staged a rally in Ohio, the most vital of the swing states, without which it would be hard for any Republican to win.
Earlier, his campaign had released an Internet and radio ad attacking Biden for chuckling and grinning during his encounter with Ryan.
"I think you might agree with me that there was one person on stage last night who was thoughtful and respectful and steady and poised," Romney told a raucous crowd in Richmond, Virginia.
Biden and Ryan – nearly 30 years his junior – tangled on Iran, Libya, Afghanistan and leading domestic issues such as health care, abortion and taxes on a combustive evening in Kentucky.
The older man sneered at the young Republican's attempts to explain the tortured mathematics of his tax policy. The Wall Street Journal described the debate as "The bully vs. the wonk."
In his turn, Biden came under intense pressure from Ryan on the administration's handling of the crisis sparked by the killing of the US ambassador to Libya, Chris Stevens, in Benghazi on September 11.
"If we're hit by terrorists, we're going to call it for what it is, a terrorist attack," Ryan said, pushing the Republican claim that Obama attempted to play down the significance of the assault. "What we're watching is the unraveling of the Obama foreign policy." – Sapa-AFP