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President Barack Obama launched a tough new pitch for what he sees as greater tax fairness Thursday in a television advertisement asserting that Republican rival Mitt Romney's economic proposals would mean cuts for the wealthiest Americans and higher payments for everyone else.

Romney hit back with a new ad timed to Obama's appearance Thursday in Florida, calling the president a "disappointment" for a statewide economic picture that has not improved under his leadership. Campaigning in Colorado later, he claimed that his economic plan would generate 12 million jobs in four years.

Economic issues are dominating the campaign because voters remain worried about the exceedingly slow recovery from the Great Recession and stubbornly high national unemployment, now at 8.2 percent. Polls show Romney, with his record with a private equity firm, leading as the candidate best qualified to deal with the struggling economy.

Obama has been trying to chip away at that lead with accusations that the firm Romney co-founded, Bain Capital, had closed down businesses it acquired and moved jobs overseas. The Republican also is pressured, even by some Republicans, for refusing to release more than just one year of completed federal tax returns.

Obama and Romney were taking their election campaigns to three of the most contested states as a bitterly divided Congress pushed toward a summer recess.

Obama was traveling to Florida and Virginia. Romney visited Colorado, where he was to appear with 10 Republican governors, some mentioned as potential running mates.

Florida is among the states hardest hit by the collapse of the housing market and has an unemployment rate of 8.6 percent, higher than the national average and tied for 39th among the 50 states. Virginia, on the other hand, has the 10th lowest unemployment at 5.6 percent.

Colorado has been struggling with a jobless rate equal to the national average of 8.2 percent. For Romney, the trip west is his first political campaign appearance since returning from an overseas trip designed to display his foreign policy credentials.

Romney vowed to make North America energy independent in eight years, saying he would emphasize drilling on public lands, coal production and the completion of an oil pipeline, but did not offer any other specifics. He said his proposals would create 12 million jobs during his term but offered no details on how that would come about.

Obama's "policies have not worked. They have not gotten America back to work again. My policies will work," Romney told hundreds of supporters gathered in the Denver area.

The new Obama ad cites a report by the nonpartisan Tax Policy Center that argues Romney has paid a lower proportion of his income in taxes than many people of lesser incomes. "He pays less, you pay more," the ad says.

The study also contends Romney's vague tax plan would result in big savings for the very wealthy while paying for the lost revenue by increasing taxes on the lower end of the income scale.

Obama also cited the study while campaigning in Orlando, where he was making up for an appearance he postponed last month after the shooting tragedy in Colorado. Orlando is in the middle of a swath of Florida that separates the Republican-leaning north of the state and the Democratic-leaning south.

Obama said Romney's plan would lead to a tax increase of more than $2,000 a year for an average family with children.

"They have tried to sell us this trickle-down tax cut fairy dust before," Obama said outside Orlando. "And guess what? It didn't work then and it won't work now."

Eric Fehrnstrom, a senior Romney adviser, called the study "a joke" and challenged its impartiality and methodology Thursday during a conference call with reporters.

Romney's response ad shows footage of Obama giving a speech in 2008 and lamenting the state of Florida's economy. The spot notes that Florida still suffers from high unemployment and record home foreclosures. "Barack Obama: What a disappointment," the ad says.

Congress helped the candidates frame the economic issues Wednesday with partisan votes on tax measures that underscored Washington's political stalemate. The Republican-controlled House of Representatives approved an extension of Bush-era tax cuts for all income levels, just a week after the Democratic-controlled Senate voted in favor of Obama's plan for continuing reduced tax rates only for households earning less than $250,000 or for individuals under $200,000.

As if to emphasize the challenge facing the presidential contenders, the Federal Reserve on Wednesday said the economy was losing strength. The next major marker of economic health is released Friday, when the government announces July hiring and unemployment trends.

Economists forecast that U.S. employers added 100,000 jobs in July. That would be slightly better than the 75,000-a-month average from April through June but still below the healthier 226,000 average in the first three months of the year.

The appearance of Romney, a former governor of Massachusetts, with Republican governors Thursday would tease speculation about his pick for a running mate. Those with him will include New Jersey's Chris Christie, Louisiana's Bobby Jindal, South Carolina's Nikki Haley and Virginia's Bob McDonnnell, all of whom have been mentioned as possible Romney picks. Absent will be two of the most often mentioned possibilities, Sen. Rob Portman of Ohio and former Minnesota Gov. Tim Pawlenty.