WASHINGTON - Mitt Romney, freed of his last serious challenger for the Republican presidential nomination, unleashed blistering attacks on President Barack Obama, assuring a brutal tone for the coming half-year of campaigning before the November election.
Rick Santorum, the former senator who had struggled under the negative advertising barrage by the better-financed and organized Romney, left the Republican race on Tuesday.
Romney, the wealthy former Massachusetts governor making his second presidential bid, intensified a full-throated assault on Obama within hours of Santorum's departure.
Campaigning in Santorum's home state of Pennsylvania, Romney portrayed Obama as a weak leader who apologizes for America's greatness and prefers European-style socialism over robust free enterprise. Obama's allies call such claims nonsense.
"The right course for America is not to divide America," Romney told a dinner gathering near Philadelphia. "That's what he's doing. His campaign is all about finding Americans to blame and attack, and find someone to tax more, someone who isn't giving, isn't paying their fair share."
Obama, campaigning in the important battleground state of Florida, said the choice this November will be as stark as in the 1964 contest between Lyndon Johnson and Barry Goldwater, which resulted in one of the biggest Democratic landslides ever. That election included dramatic moments, such as Goldwater's approval of "extremism in the defence of liberty" and a devastating TV ad suggesting a Goldwater presidency would lead to nuclear war.
Obama didn't mention Romney by name, but his top aides have shown less restraint.
Obama campaign manager Jim Messina said in a statement after Santorum's withdrawal: "It's no surprise that Mitt Romney finally was able to grind down his opponents under an avalanche of negative ads. ...The more the American people see of Mitt Romney, the less they like him."
Other Obama campaign officials have mocked Romney's wealth and called him out of touch with average Americans.
On Wednesday, Romney was asked on Fox News how he would counter continued Democratic attacks that he is an out-of-touch rich guy.
"The campaign started yesterday, the general election campaign," Romney said. "It's a little early in the process."
Romney and his allies have proved their ability to raise millions of dollars to air brutally effective attack ads. The negative assaults crippled Santorum and Newt Gingrich in primary contests. Obama will raise many millions, too, and few doubt that he will hit Romney hard.
On Tuesday, Romney made clear that he would assault Obama's character as well, saying the president is not inept at economic policy, but he actively dislikes business.
Romney made similar remarks last month. Now, with Santorum out of the way and Gingrich and Ron Paul hardly a factor, there are no intra-party distractions to dilute such comments
Obama opened a new push to revamp the U.S. tax law under which wealthy investors often pay taxes at a lower rate than middle-class wage-earners. The proposal stands little chance of passing in Congress but serves as a clear general election contrast with Romney.
"We've got to choose which direction we want this country to go," Obama told a boisterous audience of students at Florida Atlantic University.
"Do we want to keep giving tax breaks to folks like me who don't need them?" he added, referring to his own personal wealth, estimated at between $1.8 million and nearly $12 million. Romney's fortune is estimated at about $250 million.
Obama said Democrats would ensure the rich pay their fair share, while focusing on investments in education, science and research and caring for the most vulnerable. By contrast, he said, Republicans would dismantle education and clean energy programs so they can give still more tax breaks to the rich.
