Mitt Romney eked out a narrow victory in Michigan, retaining his grip on front-runner status (at least until Super Tuesday). His win in Arizona was much more decisive. The exit polls in both states show that Romney’s support came from a familiar coalition, which indicates that his intense battle with Santorum for his home state may not have jostled him as severely as some feared.

Romney did best among higher-income voters and older voters, as well as voters who identified as only somewhat conservative or moderate. His supporters appeared to be fueled mostly by belief in Romney’s electability. Santorum, by contrast, performed better among white evangelicals, very conservative voters, and voters who prioritized abortion as the most important campaign issue.

Interestingly, as David R. Jones points out at the New York Times’ Caucus blog, Arizona’s Mormons may have provided Romney with a significant edge.  In Michigan, he lost badly to Santorum among voters who believe that abortion should always be illegal (25% for Romney vs. 60% for Santorum), but in Arizona, the two nearly tied (37% for Romney vs. 42% for Santorum). Mormons, of course, hold strongly pro-life views on abortion.

Romney also trounced Ron Paul among Millennials (voters age 18-29) in Arizona, a demographic where Paul has consistently excelled. This unusual result makes sense considering that, as Jones points out, Mormon voters are much younger than the average Arizona voter.

Santorum edged out Romney among blue-collar workers in Michigan, garnering 41% of voters who make less than $50 thousand a year, compared to Romney’s 36%. Romney, meanwhile, snapped up voters who make more than $100 thousand a year, winning this constituency (which comprised one-third of the voting population) by fourteen points.

Overall, there weren’t many surprises in the Michigan exit polls. Santorum was not particularly successful in expanding his coalition beyond his base of social conservatives. Santorum shone among very conservative voters (50% vs. Romney’s 36%), voters for whom the candidate’s religious beliefs matter a great deal (63% vs. Romney’s 21%), voters who believe that abortion should be illegal (47% vs. Romney’s 38%), and voters who prioritize abortion above the budget deficit, the economy, and illegal immigration (77% vs. 13%), and voters who are looking for a “true conservative” or “strong moral character.”

Social conservatives represent a large enough chunk of the GOP primary electorate that Santorum will likely continue to have some success, particularly in certain southern states (i.e. Tennessee) but based on these primary results, he continues to lack the broad-based support that a serious contender for the GOP nomination requires.