The change in America seemed to happen so quickly that it felt like whiplash, the Odgaards said. One day they felt comfortably situated in the American majority, as Christians with shared beliefs in God, family and the Bible. They had never even imagined that two people of the same sex could marry.

Overnight, it seemed, they discovered that even in small-town Iowa they were outnumbered, isolated and unpopular. Everyone they knew seemed to have a gay relative or friend. Mr. Odgaard’s daughter from his first marriage disavowed her father’s actions on Facebook, and his gay second cousin will not speak to him. Even their own Mennonite congregation put out a statement saying that while their denomination opposes gay marriage, “not every congregation” or Mennonite does. Mrs. Odgaard, 64, the daughter of a Mennonite minister, was devastated.

“It all flipped, so fast,” said Mr. Odgaard, a patrician 70-year-old who favors khakis and boat shoes. “Suddenly, we were in the minority. That was kind of a scary feeling. It makes you wonder where the Christians went.”

The beginning of the end of the Odgaards’ familiar life came on Aug. 3, 2013, when Lee Stafford and Jared Ellars arrived at the Odgaards’ gallery, Görtz Haus. The couple were in a panic because the hotel they had booked for their wedding had gone bankrupt two months before the date, and they had already sent the invitations out. Mr. Odgaard spent about 45 minutes showing them the property and figuring out seating, flowers and how many guests needed gluten-free meals. It was only when Mr. Odgaard asked if it was a same-sex wedding that his tone changed, they said.