Doug Montzka, a contractor from St. Paul, describes himself as a devout Christian, a very conservative Republican and, only recently, a supporter of same-sex marriage.

He cannot pinpoint the moment he changed sides — his views have evolved, he says — but he does know that five years ago, he never would have voted for it.

While he trusts most everything in the Bible and knows that Leviticus condemns homosexuality as an abomination, “there’s no other reason I can think it’s wrong except the Bible,” he said.

“I’ve coached youth sports for years and had a few kids with gay parents,” said Mr. Montzka, 53. “As far as I’m concerned, if it works for them, it’s O.K. with me.”