COLUMBIA, S.C. – In a slap at his chief rival, Democratic presidential candidate Barack Obama said Thursday the most important asset the next president can offer is the ability to unite the country.

The Illinois senator did not mention Hillary Rodham Clinton, but sought to make the case the U.S. cannot afford a divisive commander in chief after George W. Bush’s two terms.

“The reason that this president has failed to lead this country is because he hasn’t been able to unite our country. He’s polarized us when he should have pulled us together,” Obama said in a speech at the College Democrats of America convention at the University of South Carolina. “That’s why the experience we need in the next president is the ability to bring this country together.

“It’s not enough to just change parties,” Obama said.

Despite being viewed unfavorably by nearly half the public, Clinton is ahead of Obama in national and most state polls in the Democratic primary race.

The New York senator’s campaign contended Obama, with his remarks, had broken a pledge “to elevate our political discourse.”

In South Carolina and during a visit to New Hampshire earlier in the day, Obama compared Clinton to Bush because, he said, she has said she will not have unconditional meetings with foreign enemies.

He told the College Democrats that her approach showed “stubbornness” and in New Hampshire he referred to her as “Bush-Cheney lite.”

Clinton said in a CNN interview that the comparison was “silly” and she questioned Obama’s adherence to the hope he preaches on the campaign trail.

“I’ve been called a lot of things in my life but I’ve never been called George Bush or Dick Cheney certainly,” she said. “We have to ask what’s ever happened to the politics of hope?”

Clinton said rushing into presidential-level meetings with the leaders of Venezuela, Cuba, Syria and Iran could put U.S. power and prestige at risk. Obama has said the U.S. should talk to everyone.

“It’s time to turn the page on an era of Bush-Cheney diplomacy and reach out to the rest of the world again,” Obama said. “Refusing to engage in tough, smart diplomacy with world leaders we don’t like doesn’t show your strength, it shows your stubbornness, and we don’t need another eight years of that.”

Both campaigns sought to play up the fight. Obama’s team sent audio of his “Bush-Cheney lite” comment to radio stations; Clinton’s camp posted video of his statement and her response on CNN on her Web site.

Later, her spokesman, Phil Singer, said Obama’s attempt to link Clinton with Bush and Cheney effectively broke his campaign promise to raise the level of political talk. “Democrats deserve better,” Singer said.

Another rival, Sen. Chris Dodd of Connecticut, criticized both sides. “There is nothing new about this kind of politics and it certainly doesn’t demonstrate a readiness to lead the nation when our reputation around the world is in tatters,” Dodd said.