PITTSBURGH >> Mitt Romney plans to stay on the attack in the race for the White House, but mounting pressure on the Republican presidential candidate to release his tax returns threatens to stunt his momentum as he courts voters across key Midwestern battlegrounds. The top Republican on Capitol Hill defended Romney on Wednesday, saying the campaign is “not about tax returns, it’s about the economy.”

Romney was taking his fight against President Barack Obama to Ohio on Wednesday, building off fiery speeches in Pennsylvania the day before in which he accused the Democrat of believing government is more vital to a thriving economy than the nation’s workers and dreamers.

“I’m convinced he wants Americans to be ashamed of success,” Romney declared Tuesday in the Pittsburgh area as hundreds of supporters cheered him on.

Having spent most of Tuesday courting donors across Texas, Obama was spending Wednesday at the White House before beginning a two-day campaign swing through Florida. His wife, first lady Michelle Obama, was speaking at a campaign fundraiser in Birmingham, Ala.

Democrats have pressed for the release of more of Romney’s tax returns and have hounded him over discrepancies about when he left his private equity firm, Bain Capital. Obama has been trying to keep Romney focused on matters other than the sluggish economy, even releasing a single-shot TV ad Tuesday that suggests Romney gamed the system so well that he may not have paid any taxes at all for years.

House Speaker John Boehner, R-Ohio, took a rare step into the presidential race Wednesday, telling 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.”

Boehner also warned those, including fellow Republicans, who are calling on Romney to make more of his 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.”