Republican presidential candidate Mitt Romney returned to Ohio on Tuesday to kick off a bus tour across this critical battleground state in a push to make up ground that he has lost to President Obama.

With polls showing Obama enjoying a clear advantage in Ohio, Romney and his running mate, Rep. Paul Ryan (Wis.), began two days of retail campaigning with a joint rally here at Dayton International Airport.

Standing in front of their campaign planes, and joined by tea party star Sen. Rand Paul (Ky.), the Republican ticket painted a dramatic contrast with the Obama administration — on their tax plans, on trade policies with China and on the size and role of government.

Romney told several hundred supporters who stood on the tarmac under gray clouds that Obama’s vision for the country is “entirely foreign to anything this nation has ever known.”

“This is a president who’s bent on growing government,” Romney added. “I am bent on growing jobs and raising take-home pay, and will do it.”

But first Romney has to win the White House, and he faces serious challenges in Ohio as well as in other important swing states. Romney’s campaign aides dismissed public polls showing the Republican at a deficit. Tuesday’s Washington Post survey found 52 percent of likely Ohio voters supporting Obama to 46 percent for Romney.

Top Romney aides predicted that the campaign’s operation on the ground in Ohio to turn out supporters could be decisive here.

“The ground game is good for a field goal. If you’re within three points, it can make a difference,” Rich Beeson, the campaign’s national political director, told reporters aboard Romney’s plane en route to Vandalia.

Beeson called Obama’s campaign “the reigning champs” because of their successful turnout operation in 2008. But, he said, with six weeks left until Election Day, the Obama campaign is too bullish.

“They’re sort of spiking the ball at the 30-yard line right now,” Beeson said. “Look, Ohio, there’s still 42 days to go. . . . we’ll be in it down to the wire and I’m confident that we will win.”

Romney hopes his bus tour, which continues Wednesday through three Ohio cities, will help generate enthusiasm for his candidacy. He has been attacking Obama on his trade policies with China, both in television advertisements and on the stump, hoping a sharp critique would rally blue-collar voters in this industrial state.

“China has cheated,” Romney said, adding, “I will not allow that to continue.”

But Obama’s campaign argued that this was simply a desperate move.

“He’s desperately trying to find something else that will ingratiate himself with working people,” former Ohio governor Ted Strickland, a co-chairman of Obama’s campaign, said in an interview. “The people in Ohio, I think, have already made up their minds about this guy one way or another, and a majority of Ohioans have concluded that he doesn’t care about them or understand them.”

Felicia Sonmez in Washington contributed to this report.