Decorah, Iowa ? Hitting back against an emboldened GOP, President Barack Obama launched a rare direct attack Monday on the Republican presidential field, criticizing his potential 2012 rivals for their blanket opposition to any deficit-cutting compromise involving new taxes.

“That’s just not common sense,” Obama told the crowd at a town hall-style meeting in Cannon Falls, Minn., as he kicked off a three-day bus tour through Minnesota, Iowa and Illinois.

“You’ve got to be willing to compromise to move the country forward,” the president said later in the day as he delivered the same message at a town hall in Decorah, Iowa.

At the same time Obama was forced to defend his own record as Iowa voters asked him about all the compromises he’s made with the GOP.

“I make no apologies for being reasonable,” Obama declared as he stood in front of a cheery red barn, surrounded by bales of hay.

The president recalled a moment in last week’s GOP presidential debate when all eight of the candidates said they would refuse to support a deal with tax increases, even if tax revenues were outweighed 10-to-1 by spending cuts.

Obama didn’t mention any of the candidates by name and prefaced the remark by saying, “I know it’s not election season yet.”

But his comment underscored that election season is indeed under way. The bus tour, although an official White House event rather than a campaign swing, is taking Obama through three states he won in 2008 but where he now needs to shore up his standing. It’s giving him a chance to return to the grassroots campaigning that helped propel him to the White House, and shed his jacket and tie to mix it up with voters in coffee shops and lunch joints far from the Beltway — as he did in three unscheduled stops Monday, including one in a tree-lined Minnesota town where he was swarmed by enthusiastic kids.

The president is traveling in an imposing new $1.1 million bus, outfitted with tinted windows and flashing lights, that the Secret Service purchased.

In Iowa, Obama returned to a state that handed him a key victory over Democratic rival Hillary Rodham Clinton in their nomination fight but where Republicans have now been blanketing the state in preparation for its first-in-the-nation caucuses, attacking the president at every turn. The bus tour came on the heels of Rep. Michele Bachmann’s weekend victory in the Iowa Straw Poll and Texas Gov. Rick Perry’s contest-rattling entrance into the race.

It also came after the president spent much of the summer holed up in the nation’s capital enmeshed in bitter, partisan negotiations on the debt crisis that cratered his approval ratings and those of Congress amid a faltering economy and high unemployment.

The president got a rosy reception from his Minnesota audience, but Iowa voters were a tougher crowd, demanding to know why he’d compromised on principles important to Democrats, and asking to hear his plans for dealing with intransigent Republicans.

The president responded by pledging to present a specific jobs plan to Congress when lawmakers return from their summer recess in September. “And if they don’t get it done, then we’ll be running against a Congress that’s not doing anything for the American people and the choice will be very stark and very clear,” the president said.