Caleb Campbell, a pastor at Desert Springs Bible Church, attended several Turning Point USA events over the past year.Joe Rondone/The Republic/Reuters You can think of Donald Trump’s most faithful adherents as bigots or patriots, constitutional standard-bearers or deluded masses. Caleb Campbell likes to think of them as sheep that have gone astray. He has made it is his work to lead them back. Mr. Campbell is a pastor at Desert Springs Bible Church in Phoenix. But for much of the last year he has been an undercover man of the cloth, using his pastoral credentials to gain entry to the...