MAPLEWOOD, Minn. — Like most pastors who lead thriving evangelical megachurches, the Rev. Gregory A. Boyd was asked frequently to give his blessing — and the church’s — to conservative political candidates and causes.The requests came from church members and visitors alike: Would he please announce a rally against gay marriage during services? Would he introduce a politician from the pulpit? Could members set up a table in the lobby promoting their anti-abortion work? Would the church distribute “voters’ guides” that all but endorsed Republican candidates? And with the country at war, please couldn’t the church hang an American flag...