NORTH CHESTERFIELD, Va. – President Barack Obama wrapped up a three-day bus tour through two politically potent Southern states Wednesday, delivering a potential preview of a 2012 campaign theme: insisting he's trying to deliver a jolt to the moribund economy but is being thwarted by Republicans who want only to roll back financial and environmental regulations.

At Fire Station 9 here, Obama stood on a stage flanked by a yellow firetruck and two lines of uniformed firefighters, and insisted that Republicans who vote against his $447 billion jobs package will owe the American people an explanation.

"They're going to have to come down here and tell folks in Virginia and all across the country why people are going to have to cope with fewer first responders, why your kids can't have teachers back in the classroom," he said. "You're going to have to look construction workers in the eye and tell them why they're sitting idle instead of rebuilding infrastructure that we know needs to be rebuilt."

But back in Washington, Senate Republicans showed little interest in embracing the jobs package, which includes $30 billion in aid to cities and towns to keep schoolteachers and firefighters on the job.

Senate Minority Leader Mitch McConnell of Kentucky took to the Senate floor to decry the bus trip, calling it "completely preposterous" for Obama "to be riding around on a bus saying we should raise taxes – on the very folks who create jobs."

"Let's park the campaign bus, put away the talking points and do something to address this jobs crisis," McConnell said.

Republicans oppose the tax increases on millionaires that Obama proposes to pay for the package and say tax breaks should be considered instead.

Traveling aboard the high-tech black bus that Obama quipped was "not your normal RV," the president spent the final day of his trip in Virginia, a state he won in 2008 but where polls suggest he faces a steep climb to recapture what had long been a Republican-leaning state in presidential elections.

White House spokesman Jay Carney dismissed McConnell's criticism that Obama should not be out on the road.

"Presidents can and should get out of Washington on occasion to meet with ordinary Americans and hear from them about the challenges they face in this difficult economy," Carney said.

First lady Michelle Obama joined the president earlier in the day, lending her star power to announce before a military audience in Hampton, Va., that more than 250 U.S. companies have pledged to hire 25,000 veterans and military spouses by the end of 2013.

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