Santorum-Romney battle reveals stark divide in the GOP As Santorum closed out his rally Friday night, he sounded as if he were looking for a political miracle. "You can turn this race completely on its head," he said. No one is expecting us to do well in Illinois. Why is a state like Illinois so potentially difficult for Santorum? He once led the polls in both Michigan and Ohio, two other Midwestern industrial states, and one poll taken little more than a week ago showed him within a few points of Romney here. But in the end he fell short in those two other heartland battlegrounds. He could be heading toward the same outcome on Tuesday, as more recent polls are suggesting. So much has been written about frontrunner Mitt Romney's inability to put away his rivals with greater ease and why he hasn't wrapped up the nomination more quickly. But another part of this contest is why it may not be possible for Santorum, the candidate seemingly most in tune with the Republican base, to overtake Romney, who has been unable to win over significant portions of that base. The reasons only partly relate to Romney's or Santorum's skills as a candidate, or even the huge differential in resources. What now defines the contest for the Republican nomination are the demographics of today's Republican Party. Whatever weaknesses people ascribe to Romney or Santorum as candidates, the Republican race is turning on the economic and religious divides in the GOP coalition. That's why states like Illinois, Michigan and Ohio are difficult for Santorum and states like Mississippi, Alabama and Tennessee were hard for Romney. Santorum is the candidate of evangelical Christians, voters who are very conservative and Republicans who make less than $100,000 a year. Romney consistently does best among those making more than $100,000 a year, non-evangelicals and Republicans who say they are only somewhat conservative or moderate or liberal. You can see the two parts of the party at the rallies of the two candidates. Santorum's on Friday was held at the Christian Liberty Academy. The audience, more than 1,000 strong, included parents with small children, young families, people who said they were struggling economically. Romney's rallies look and feel different, less overtly religious with fewer references to social issues by the introductory speakers. Santorum stresses his blue-collar roots, but in his speeches he talks less about jobs and more about freedom, less about tax cuts and small business incentives and more about the cultural differences he has with Obama. He talks about family and invokes God as a central force in America success. Romney focuses primarily on jobs and economic themes.