The two dozen pastors gathered in a dreary room adorned with balloons and needlepoint texts from Scripture, deep within the cavernous Greenwell Springs Baptist Church. They had come from as far as Texas and Colorado to this red-brick building on the outskirts of Baton Rouge, La., at the behest of Tony Perkins, one of America's most influential evangelical Christian leaders. And their host made clear that the evening's guest of honor had his blessing. "I wouldn't invite just anybody to my church," Perkins said as he introduced Rick Santorum.
It was the Sunday before the Louisiana primary on March 24. The...