Santorum later explained his comments as being about freedom, not the economy.
"The problem with the economy is government taking people's freedom away and advancing regulations, destroying and undermining businesses ability to be problem solvers," he told Chicago radio station WLS. "Americans don't take kindly to the yoke of government, and we don't do very well. Our economy struggles when that happens"
Romney, meanwhile, campaigned in the city where Obama taught law at the University of Chicago and where the president has his national campaign headquarters. Avoiding any reference to Republican opponents during his afternoon speech, Romney assailed the president.
"The American economy is fueled by freedom," he said, flanked by a row of American flags. "The Obama administration's assault on our economic freedom is the principal reason why the recovery has been so tepid — and why it couldn't meet their expectations, let alone ours."
At the current primary election rate, Romney would capture the nomination in June unless Santorum or Gingrich wins decisively in the coming contests. Including Puerto Rico's results, Romney has now collected 521 delegates, compared to Santorum's 253, Gingrich's 136 and Paul's 50, according to an Associated Press tally.
Romney and a growing number of Republicans across the country are eager to move beyond the increasingly nasty primary season that has consumed far more energy, resources and political capital than most expected. But the former Massachusetts governor has so far struggled to win over his party's most passionate voters — tea party activists and evangelicals who don't trust him as a true conservative.
Romney's wife, Ann, had called for Republicans to unite behind her husband at a campaign stop the night before, suggesting it was time to "move on to the next challenge."
Indeed, the battle for Illinois comes as Obama's campaign builds a mountain of campaign cash and organization in key states.
Obama collected $45 million for his re-election bid in February, accelerating his fundraising pace as his campaign fretted over an oncoming spending blitz by Republican-leaning outside groups.
With Republicans locked in their extended primary campaign, Obama's team is building a 50-state operation that aims to help register new voters, bring back past supporters and boost turnout. Obama's campaign had about $75 million in the bank through the end of January, but totals for February were not immediately available.
Romney and Santorum, by comparison, raised $11.5 million and $9 million respectively in February. And Romney and his allies are spending large amounts in Illinois.
Romney's campaign had spent $1.1 million, while the pro-Romney super PAC, Restore Our Future, had spent an additional $2.4 million on advertising in Illinois through Monday, according to figures collected by the media monitoring firm, SMG Delta. Santorum's super PAC, the Red White and Blue Fund, had spent $327,000, while his campaign had spent $200,000.
Each side bought television ads that attacked the other. And though Romney focused on Obama Monday, he had spent much of the previous week calling Santorum "an economic lightweight," an indication that he continues to view Santorum as a threat.
Associated Press writer Don Babwin in Rockford, Ill., contributed to this report.
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