Ten states are voting today in the Republican primary. One of the most important votes that Gingrich, Romney and Santorum have spent a lot of time courting are evangelicals.
Classically, the group turns out in large numbers and is great at backing one candidate.
But this year they're split between the top two GOP contenders: Santorum and Romney.
And whoever they end up backing could win in a lot of key states.
For example, four years ago, 70 percent of primary voters in Tennessee and Oklahoma were evangelicals.
John Green is the Director of the Bliss Institute at The University of Akron and an expert on religion in American Politics.