President Obama introduced a new word into the American political lexicon Friday, accusing his GOP opponent, Mitt Romney, of “Romnesia” for changing positions and trying to pivot to the political center.

Before nearly 10,000 supporters at a Virginia rally, Obama smiled, joked and wagged his finger as he mocked Romney’s earlier declaration that he was a “severely conservative” governor of Massachusetts.

“Now that we’re 18 days out from the election, ‘Mr. Severely Conservative’ wants you to think he was severely kidding about everything he said over the last year,’’ Obama said in a speech devoted almost entirely to attacking Romney, and during which he gave little indication of what he would do in a second term if reelected.

Building in intensity, Obama continued: “He’s forgetting what his own positions are, and he’s betting that you will, too. I mean, he’s changing up so much and backtracking and sidestepping. We’ve got to — we’ve got to — we’ve got to name this condition that he’s going through. I think — I think it’s called ‘Romnesia.’ ”

The crowd roared.

The Romney campaign was not amused. “America doesn’t need a comedy routine; it needs a serious plan to fix the economy,’’ Romney senior adviser Danny Diaz wrote on Twitter.

Added Amanda Henneberg, a Romney spokeswoman: “Women haven’t forgotten how we’ve suffered over the last four years in the Obama economy with higher taxes, higher unemployment, and record levels of poverty. President Obama has failed to put forward a second-term agenda — and when you don’t have a plan to run on, you stoop to scare tactics.’’

The renewed skirmishing came as the other candidates converged on the key swing state of Florida ahead of Monday’s final presidential debate in Boca Raton, which is shaping up as critical in a race that polls show is tight nationally and in battleground states.

Vice President Biden and Romney’s running mate, Rep. Paul Ryan (R-Wis.), spent their Friday rallying supporters in the Sunshine State, whose 29 electoral votes make it the biggest swing state prize. At one point, Ryan’s campaign jet rolled across the tarmac in Tampa past Biden’s Air Force Two.

Ann Romney and Michelle Obama, both important surrogates as the campaigns battle for an edge among women voters, have events scheduled for South Florida in the coming days. Female voters are a critical bloc that could determine who is elected on Nov. 6, and recent polls have shown Romney cutting into Obama’s lead among them.

With the economy still the key issue in the race, Obama got some potentially good news on Friday: New data from the Bureau of Labor Statistics showed that the unemployment rate dropped in 41 states last month, including many of the top swing states. Those included Florida, Colorado and Iowa. Yet Florida’s rate, at 8.7 percent, remains higher than the national average, and unemployment is still high across the country.

Romney prepared for the debate Friday morning in New York before flying to Florida. where he appeared with Ryan at a rally in Daytona Beach in the evening.

They spoke to a crowd of thousands of supporters who were warmed up to the singing of country music star John Rich of the group Big and Rich.

Romney said that Obama’s reelection effort has become the “incredibly shrinking campaign.”

“Have you been watching the Obama campaign lately. It’s absolutely remarkable,” Romney said. “They have no agenda.”

But speaking to the tightness of this race, even as Ryan and Romney spoke, a crowd of Obama supporters gathered and shouted “Obama. Four More Years,” drowning out parts of Romney’s 20-minute speech.

Romney’s debate partner, Sen. Rob Portman, as well as top advisers Stuart Stevens, Beth Myers and Dan Senor joined him on the flight to Florida.

It was Romney’s commanding performance in the first presidential debate two weeks ago — along with Obama’s widely panned showing — that reconfigured a race in which the president had been ahead.

Romney on Friday released a new television ad titled “Bringing People Together.” It emphasized his bipartisan credentials, though some Democrats in Massachusetts say Romney worked only sporadically with them during his governorship. But the Romney campaign also apparently senses vulnerability on the subject for Obama, whose political brand in his 2008 campaign was built around his ability to transcend partisan divides.

Yet it was a highly partisan president who spoke on Friday in an open field at George Mason University in the critical battleground state of Virginia. Obama drew chants of “Four more years!” as he bounded onto a podium draped with two blue signs reading “Women’s Health Security.’’

Obama portrayed Romney as a “throwback to the 1950s” who would restrict women’s rights, favor the wealthy and squeeze the middle class.

During his riff on what he called “Romnesia,’’ Obama said: “I’m not a medical doctor, but I — but I do want to go over some of the symptoms with you because I want to make sure nobody else catches it.’’

The crowd hooted.

Obama then listed a series of what he called position changes by Romney, focusing on women’s issues. “You know, if you say you’re for equal pay for equal work, but you keep refusing to say whether or not you’d sign a bill that protects equal pay for equal work, you might have ‘Romnesia,’ ’’ Obama said. “If you say women should have access to contraceptive care, but you support legislation that would let your employer deny you contraceptive care, you might have a case of ‘Romnesia.’ ”

The president drew his loudest applause by bringing up the Affordable Care Act, also known as Obamacare. Chuckling, he said: “If you come down with a case of ‘Romnesia’ and you can’t seem to remember the policies that are still on your Web site, or the promises that you’ve made over the six years you’ve been running for president, here’s the good news: Obamacare covers preexisting conditions.’’

“We can fix you up. We’ve got a cure. We can make you well, Virginia. This is a curable disease.’’

Nia-Malika Henderson, Felicia Sonmez and Philip Rucker contributed to this report.