They remain his base. CBS News reports:
Santorum kept the race close in Ohio by doing exceptionally well among socially conservative voters. Four-in-ten Republican primary voters in the state identified themselves as very conservative on issues such as gay marriage and abortion. These social conservative voters strongly preferred Santorum to Romney 53 percent to 25 percent.
Evangelical Protestants, not Catholics, was the religious group most supportive of Santorum. Evangelical Protestants preferred Santorum over Romney 49 percent to 29 percent. Santorum, though, was defeating among those who shared his faith, losing the Catholic vote to Romney 44 percent to 31 percent.