Senator Rob Portman of Ohio, one of the most respected and comparatively moderate Republicans in Congress, has had a change of heart on same-sex marriage. The reason for Portman's change of heart is that his son is gay, and he wants his son to be happy. And happiness means the ability to get married, as straight couples can.

This is all to the good. But how many Republican elected officials will have to discover they have gay children for the party to relent on its unyielding position against same-sex marriage?

Portman isn't so much an evangelical conservative as a fiscal one. Still, there was little advantage for him in supporting same-sex marriage -- at least until he learned that his 21-year-old son, Will, is gay. Will told his parents two years ago, and he agreed that it was time to have his father go public with his change of heart. In an interview with CNN, Portman said he has always been supportive of his son -- privately.

Portman said he told the presidential campaign of Mitt Romney about his son when he was being vetted for vice president last year. He didn't get the nod, but said the campaign told him it wasn't because his son was gay.

This is reminiscent of another high-ranking official with a gay child whose views softened on same-sex marriage while in office -- and changed when he left. Former Vice President Dick Cheney quietly followed the party line on same-sex marriage, never making it a big issue but not bucking it, either.

In 2000, in the vice presidential debate with Senator Joe Lieberman, Cheney discussed his love for freedom and privacy in the bedroom. "People should be free to enter into any kind of relationship they want to enter into," he said. "It's no one's business." When his daughter, Mary, and her partner had a boy in 2007, the proud grandfather posed with the baby for a White House photo. In 2009, Cheney said that he favors gay marriage but would leave its legalization up to the states.

For many gays, living happily ever after isn't possible, in part because of the Republican Party's opposition to same-sex marriage. Waiting for every elected Republican official to have a personal epiphany is a slow and inefficient way to change party policy, no matter how moving or satisfying the stories may be. If Rob Portman wants Will Portman to be accepted in the Republican Party, then Dad has some work to do. 

(Margaret Carlson is a Bloomberg View columnist. Follow her on Twitter.)