Iowa evangelicals could play an unfamiliar role in 2016: Putting down an insurgent Republican candidacy rather than boosting one. This is a crucial demographic in the country's first nominating contest. According to the 2012 entrance polls, 57 percent of last time's caucus-goers were evangelicals or born-again Christians. Typically, these Iowa voters have helped insurgencies. In 1988, Pat Robertson ran ahead of George H.W. Bush in all 99 counties. Pat Buchanan barely lost the state to Bob Dole in 1996, setting him up for victory in New Hampshire. In 2008 and 2012, Iowa evangelicals launched Mike Huckabee and Rick Santorum from...