In the final hours before Tuesday's Illinois primary, the top two Republican contenders talked about two different presidents.

Former Massachusetts Gov. Mitt Romney, who holds a lead in the polls, ventured into President Barack Obama's home turf Monday to assail the president's economic policies and to pledge a fidelity to deregulation if elected.

"The Obama administration's assault on our economic freedom is the principal reason why the recovery has been so tepid," he said during a speech at the University of Chicago where Obama once taught. "If we don't change course now, this assault on freedom could damage our economy and the well-being of American families for decades to come."

While Romney mentioned Obama by name numerous times throughout the speech, he ignored by name his main rivals for the GOP presidential nomination.

Romney is hoping that a decisive win in Illinois will allow him to portray himself as the inevitable adversary for Obama. But this is a strategy Romney has tried to use before, tackling the president after a win in Florida, only to be sucked back into the primary brawl when top challenger Rick Santorum began to surge. Two other candidates, Newt Gingrich and Ron Paul, lag far behind in Illinois.

Santorum on Monday spoke about a different president, visiting the boyhood home of Ronald Reagan in Dixon, Ill. Santorum's blunt message as he stood before a Reagan statue: I'm the best candidate left in the field to represent true conservative principles. The former senator from Pennsylvania even compared his underdog fight this year with Reagan's 1976 primary battle against President Gerald Ford.

"Reagan ran that insurgent campaign in 1976," Santorum said, "and people said, 'Why don't you get out of the race? You don't have a chance of winning.' And he fought."

Santorum compared Romney to the then-incumbent Ford by calling Romney "someone that is certainly the choice of the establishment Republican, someone who's 'turn it was.' We see that so often in Republican politics for president."

Reagan went on to lose to Ford, which, Santorum reminded his supporters in Dixon, led to Jimmy Carter's four years in the White House.

While arguing that he has the best business experience to right the nation's fiscal ship, Romney did get a jab in at Santorum: He said the Republican Party is "not going be successful in replacing an economic lightweight if we nominate an economic lightweight."

Santorum responded on Monday by arguing that there is something "more foundational going on" with his campaign than unemployment rates and growth rates. He said the issue of the race is not about the economy but about the federal government oppressing people and taking away their freedoms.

"We have one nominee who says he wants to run the economy," Santorum said, "What kind of conservative says that the president runs the economy? We conservatives generally think that government doesn't create jobs."

The back and forth at two different events on the last day before the primary highlighted the fundamental differences between the two candidates.

Santorum, a Catholic, often begins his speeches by talking about his faith. He told Sunday crowds that he didn't come to "to give a political speech; I'm here to share with you a little bit about my journey and my life as a Christian." His choices for venues often include churches and Christian schools.

More than 2,000 people gathered last Friday night at Christian Liberty Academy in the Chicago suburbs of Arlington Heights to hear Santorum speak. He drew applause that night by mentioning that his children had been taught through a combination of homeschooling and Christian schools. Santorum then talked about the journey he and his wife took while praying over the decision to make a presidential run.

"This is what we were called to do," he told the crowd before later arguing that Obama does not stand for the nation's values overseas or at home. Santorum claims he is carrying the "freedom agenda" for this election.

Romney has tread lightly on the social issues while hitting the economy hard. He uses his business and executive background as proof that he is the best candidate to undo policies of the Obama administration that have left it "much more difficult, if not impossible" for those dreaming about building their own business.

"This for me is not, by the way, something I've just read about," Romney said. "This is not something I learned about in a subcommittee of Congress. This is something I experienced. I've lived my life in the real economy."