Democrats Shake Up Michigan Primary, Exit Polls Show Michigan's primary drew the Republican Party's ideological, religious and socioeconomic divisions in sharp relief, raising questions both for the primaries ahead and for the party's ability to coalesce behind its eventual candidate. But it was voters of another stripe entirely - Democrats - who made things especially interesting. In what could be the closest primary to date this year, Rick Santorum easily won the groups he's targeted, including strong conservatives, evangelicals, strong Tea Party supporters and ardent abortion opponents. Union voters, fleeing Mitt Romney, also helped Santorum. And so did Democrats. Exit poll results found that nearly one in 10 voters in Michigan's open primary were Democrats. That was off their peak - 17 percent in 2000, when they tipped the contest to John McCain. But they influenced this year's outcome nonetheless: Santorum won 53 percent of Democrats, versus just 17 percent for Romney. Without them Romney would have had a fairly comfortable win. With them, it was closer. For his part, Romney relied on some of his customary support groups, notably wealthy voters and senior citizens - effective elements, if not necessarily the most compelling ones, for a national campaign. He won senior citizens, but no other age group. He won $100,000-plus voters, but no other income group. He especially won $200,000-plus voters, a group around which it's hard to build a slogan for the masses. Indeed, in a result suggesting that Romney won more heads than hearts, he beat Santorum by a 2-1 margin, 52-26 percent, as the candidate seen as most likely to defeat Barack Obama in November. Yet the contest between the two in this primary was a far closer one than that. In another exit poll result, showing a less than fired-up electorate, fewer than half of voters, 45 percent, said they were strongly behind their candidate. More voters instead said they either liked their man with reservations (38 percent) or chiefly disliked the other guy (15 percent). Just half of Romney's supporters, and fewer of Santorum's - 38 percent - strongly favored the candidate they voted for. In the night's other contest, Romney had a far easier ride. In Arizona his campaign was largely unanswered by Santorum. Romney ran competitively in the groups in which he's shown vulnerability this cycle - and that he lost in Michigan. He and dominated in other, less ideological groups. He also benefited from the largest share of early-deciders this cycle. In Michigan, after painting Santorum as a tool of "big labor," Romney lost voters from union households to the former Pennsylvania governor by 27-45 percent. That may have been intentional; union members made up a slipping share of Michigan GOP primary voters (down from 34 percent in 2000 to 23 percent this year), and Romney appeared to reach instead for the larger non-union vote. He won it - but by just an 8-point margin. Ideologically, about six in 10 Michigan voters described themselves as conservative, evenly split between "very" and "somewhat" conservative. Very conservatives went to Santorum by 50-35 percent; their less ideological brethren, to Romney by an almost identical margin, 50-31 percent. Moderates may make the difference, presumably not the group most Republicans prefer to have pick their nominee. Santorum won evangelicals, a group among which Romney, a Mormon, has struggled, by a wide 50-32 percent. Along with very conservatives, it's another potentially ominous result for Romney in the Southern primaries ahead. Santorum won voters who care a "great deal" that a candidate shares their religious beliefs by a vast 42 points, and those who want abortion illegal in all cases by a nearly as vast 33 points. But he has his own challenges in these results - voters with less emphatic views on those two questions went for Romney.