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A defiant Mitt Romney brushed aside more calls for the release of his tax returns on Wednesday and instead accused President Barack Obama of protecting his job at the expense of millions of unemployed Americans.

Intensifying his attacks as Obama focused on official meetings in Washington, the Republican presidential candidate told an overflowing Ohio crowd that the Democrat hasn't met with his jobs council in more than six months. In that time, however, Romney says Obama held 100 fundraisers.

"His priority is not creating jobs for you," Romney declared in Bowling Green. "His priority is trying to keep his own job. And that's why he's going to lose it."

For the often-reserved Romney, the fiery rhetoric marks an aggressive shift as he struggles to answer questions about his business career and personal tax returns. The former businessman, who would be among the nation's wealthiest presidents if elected, has broken from tradition so far, having released just one year of personal income tax returns and promised to release a second.

But in speeches across four states this week, Romney has thrilled supporters with aggressive attacks on Obama and charges of "crony capitalism." At the same time, the Republican's campaign has teased reporters with news that Romney's selection of a running mate could come any day, forcing new attention on what may be the most important decision of the campaign so far.

National polls suggest that the candidates are locked in a tight race less than four months before voters weigh in. Obama was expected to return to campaigning Thursday for a two-day swing though Florida.

The growing war of words between the campaigns drew a response from House Speaker John Boehner, R-Ohio, who took a rare step into the presidential race Wednesday.

Congress' top Republican told reporters in Washington that Obama's criticism of Romney's career and taxes are meant to distract from the administration's handling of the economy. Boehner said Obama's questions are an "attack on the private sector" and show that the president "doesn't give a damn about middle-class Americans who are out there looking for work."

The speaker also offered a warning for those, including fellow Republicans, who are calling on Romney to make more tax returns public. "The American people are asking, 'Where are the jobs?'" Boehner said. "They're not asking where the hell the tax returns are. It's not about tax returns, it's about the economy."

The warning didn't quiet the critics of Romney's stand on tax returns.

"If you're going to run for president, it's not necessarily comfortable but it has become a tradition and it's an important one, you make your tax returns available because you think the American people deserve that kind of transparency," Obama spokesman Jay Carney told reporters.

Several high-profile Republicans joined the call for transparency, including Maine Sen. Olympia Snowe, Indiana Sen. Richard Lugar, Iowa Sen. Chuck Grassley, Georgia Sen. Johnny Isakson, and Texas Gov. Rick Perry, who challenged Romney for the GOP nomination earlier in the year.

Perry, who released his tax returns dating back to 1992, said anyone running for office should make public as much personal information as possible to help voters decide. In an editorial, the conservative National Review also urged Romney to release more tax returns even though it agreed with him that Obama's camp wanted them for a "fishing expedition."

The Romney campaign concedes that many voters would prefer transparency but doesn't believe that the issue is important enough to sway votes in November. And it offered a multipronged counterattack Wednesday.

Former Minnesota Gov. Tim Pawlenty, who features prominently in speculation about Romney's choice for a running mate, vigorously defended Romney's position.

"There is no claim or no credible indication that he's done anything wrong," Pawlenty said on "CBS This Morning."

Senior Romney aide Eric Fehrnstrom refused to talk about the issue when asked about it before Romney's rally in Bowling Green. "That's been discussed ad nauseum," he said in declining to respond to Carney's comment.

The single year of tax returns released by Romney show investments and off-shore accounts scattered across the globe, including Switzerland and Grand Cayman.

But Romney's newfound aggression forced the Obama team to answer some uncomfortable questions as well. Asked why the president's jobs council has not met for six months, Carney said there was no specific reason.

"The president has obviously got a lot on his plate," Carney told reporters. "But he continues to solicit and receive advice from numerous folks outside the administration about the economy, about ideas that he can act on with Congress or administratively to help the economy grow and help it create jobs."

Romney also released a TV ad accusing Obama of sending tax dollars overseas. The ad says Obama sent stimulus money to "friends, donors, campaign supporters and special interest groups" and charges that taxpayer dollars went to projects in Finland and China.

Romney also seized on comments Obama made last week in Virginia.

Addressing the role of government in the American economy, the president said, in part: "Somebody helped to create this unbelievable American system that we have that allowed you to thrive. Somebody invested in roads and bridges. If you've got a business, you didn't build that. Somebody else made that happen." He added: "The point is, is that when we succeed, we succeed because of our individual initiative, but also because we do things together."

Romney lashed out at the remarks while in Bowling Green, in keeping with a strategy his campaign says will be a theme for the week, if not longer.

"This is the height of foolishness," Romney said. "Barack Obama's attempt to denigrate and diminish the achievement of the individual diminishes us all." He continued the line of criticism during a fundraiser Wednesday evening in Canton, Ohio.

Meanwhile, speculation grew about Romney's selection of a running mate. In Bowling Green, he was asked for assurances that he would select a conservative vice president.

"I can assure you that even though I have not chosen the person who will be my vice president, that person will be a conservative," Romney said. "They will believe in conservative principles."

Earlier in the day, Romney's wife, Ann, shed some light on the vice presidential search. In an interview with ABC News, scheduled for broadcast Thursday, Ann Romney said her husband had yet to settle on a candidate.

"We are certainly talking a lot. This last week, this last weekend, there was a lot of discussion," she said, according to excerpts released by the network. "There was a lot of talk. We're not quite there yet. And we're going to be there soon."

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Associated Press writers Laurie Kellman and Ben Feller in Washington and Thomas J. Sheeran in Canton, Ohio, contributed to this report.