Chicago ? His confidence surging, Mitt Romney pointedly ignored his Republican rivals on the eve of today’s high-stakes primary election in Illinois and turned his fire instead on the Democrat he hopes to oust in the fall.

Romney pushed into President Barack Obama’s home territory, assailing Obama’s economic credentials on the Chicago campus where the president taught for more than a decade.

“Freedom is on the ballot this year,” Romney told students and supporters, contending that the nation’s recovery from recession was being limited by an “assault on our economic freedom” by Obama. “I am offering a real choice and a very different beginning,” he said.

While Republican rival Rick Santorum courted anti-Romney conservatives across Illinois, the front-runner was trying to show he was more than ready to rise above the grinding GOP primary battle and move toward a general election matchup against Obama. Romney has secured more delegates than his opponents combined, and his nomination seems more assured each week as Santorum’s shoestring campaign struggles under the weight of continued disorganization.

But a victory in Illinois’ primary today is by no means assured.

Romney has spent big on advertising here, and he will have devoted more than three straight days to the state by the time votes are counted tonight.

After embarrassing Santorum with a one-sided victory in Puerto Rico Sunday, the Romney campaign sees in Illinois a potential breaking point for stubborn rivals who have defiantly vowed to stay in the race until the GOP’s national convention in August. Should Santorum and Newt Gingrich stay politically alive until then and follow through on their threat, it could turn the convention into an intra-party fight for the first time since 1976.