Tony Campolo is a Baptist clergyman and university sociologist, has written a series of books and was a counselor to President Clinton during the Monica Lewinsky scandal.
All during his career, he's been involved in skirmishes with other clergy, including an informal heresy hearing.
While strongly in favor of clergy being involved in issues, he says backing candidates crosses the line.
"There's a big difference between dealing with issues and endorsing candidates," Campolo said.