Economy is Romney's battleground
Mitt Romney is betting his message of economic expertise will echo with Republican voters in Illinois, overcoming Rick Santorum's sharply honed conservatism in their increasingly bitter contest.
Both men are competing for the 54 delegates at stake in the heartland state, one of the last major primary and caucus battlegrounds before a three-week lull in April.
Mr Romney's confidence was on display, while Mr Santorum was forced on the defensive for first declaring that the economy was not a top issue in the campaign and then saying that "the campaign doesn't hinge on unemployment rates."
By the end Mr Santorum had conceded that the economy and unemployment were important but said they were symptoms of what he described as broader ills: government intrusion and eroding freedom.
Mr Romney denounced president Barack Obama's economic policies, choosing to make his remarks at the university where the president once taught constitutional law.
Mr Santorum, however, turned his fire on Mr Romney, who leads the Republican field in delegates and whose nomination, barring a political disaster, seems increasingly assured as the contest results mount. Mr Santorum cloaked himself in the mantle of former conservative president Ronald Reagan and argued that Mr Obama's health care reforms, not the economy, were the predominant issue of the campaign.
The Illinois primary comes on the heels of Mr Romney's overwhelming victory on Sunday in Puerto Rico.
Even if he should lose the popular vote, Mr Romney is poised to win the delegate battle. Mr Santorum cannot win at least 10 of the state's 54 delegates available because his campaign did not file the necessary paperwork.
The contest next moves to Louisiana, a state in the deep South where Mr Romney has had trouble breaking through. Louisiana has a total of 46 delegates to the Republican National Convention, but only 20 delegates are at stake in Saturday's primary. An additional 23 delegates will be selected at the party's state convention in June, and the remaining three are the automatic Republican National Committee delegates.