Senator Rob Portman of Ohio now supports same-sex marriage, saying his personal views were affected by his son’s coming out two years ago.

First of all, good for Rob Portman. If he’d reacted negatively when his son came out to him, he certainly would not have been the first opponent of gay rights to do so. It feels weird to compliment Portman for treating his own child with decency, but many parents of gays and lesbians fail on this front. Portman didn’t, and for that he deserves credit.

Indeed, Portman has not only accepted his son but publicly changed his views on gay rights at potentially significant political cost. He has often been discussed as a possible Republican presidential contender; this will surely make it impossible for him to be nominated for president or vice president in 2016, and he will probably face an anti-gay-marriage challenger when he seeks re-election in three years. Portman has to know that what he did today was the opposite of politically expedient, and he did it anyway.

So I think Jonathan Chait is being hugely and unnecessarily uncharitable when he describes Portman’s move as “selfish.” Chait takes this as Portman deciding that public policy should serve the personal interests of his family; I read it more as Portman’s family experience causing him to feel greater empathy with gays and lesbians in general. He doesn’t want to change policy to make his family happy. His changed understanding of what makes his family happy has changed his understanding about what makes families in general happy.

That said, Portman’s reliance on family experience reflects a problem. So many of the moving speeches we have seen from Republican state legislators explaining why they support same-sex marriage have had to do with their gay relatives.  Politicians are not alone in letting their personal interactions with gays and lesbians shape their views on gay rights. In 2009, a Gallup poll found that knowing a gay or lesbian person personally hugely affected one's views on same-sex marriage and sodomy laws.

Unlike members of the general public, it is an elected official’s job to consider the needs and rights of everyone, not just the people immediately around him or her. We shouldn’t have to wait for people like Mary Cheney to come along and trigger Republican politicians’ empathy; they should care about gay people even if their relatives aren’t gay.

There's another way of looking at the gay-relative effect, however. The push from inside the family isn’t just about bridging an empathy gap; it also helps Republican politicians who would like to support same-sex marriage bridge a political gap. Having a gay son will actually make it easier politically for Portman to support same-sex marriage. His opponents will temper their attacks on him for fear of being seen to attack his son; voters skeptical of same-sex marriage may still relate to Portman’s choice to stand up for his family.

I’m reminded of a 2010 interview of Charlie Baker, then seeking the Republican nomination for governor of Massachusetts, with a conservative talk show host. Baker was asked why he supported same-sex marriage, and he responded by talking about his gay brother and how it was a personal issue for him. The host moved on.

Now, I doubt Baker’s gay brother mattered at the margin in his support for same-sex marriage. All living Republican ex-governors of Massachusetts, except the ones named Mitt Romney, support same-sex marriage. Baker was a top staffer in the administration of former Governor Bill Weld, who was arguably the most pro-gay governor of either party in the early 1990s. Shortly after same-sex marriage was legalized in Massachusetts, Weld delivered the homily at the gay wedding of two officials who had served alongside Baker. Baker picked a gay state legislator as his running mate.

But by framing the issue around his brother, Baker made same-sex marriage personal not just for himself but also for the questioner. It’s almost a dare: “What are you going to do, attack my family?” And just as personalization is important for supporters of same-sex marriage, abstraction is important for opponents. It’s a lot easier to oppose same-sex marriage if you pretend the gay people hurt by the policy don’t actually exist. Portman’s gay son allows him to put same-sex marriage opponents on uncomfortably personal turf.

And that leads to my final thought: I hope Portman can help to change this landscape, and help Republicans who don’t have gay children change their minds on same-sex marriage.

Just a week and a half ago, I was lamenting on MSNBC that Republican supporters of same-sex marriage, as compiled in the recent amicus brief put together by former party chairman Ken Mehlman, are almost exclusively ex-officials or behind-the-scenes players: that is, people who will never have to face a Republican primary electorate. Now Portman, by far the most prominent Republican elected official to support same-sex marriage, has become an enormous exception to that rule. His example -- and his activism -- could help to create future exceptions.

(Josh Barro is lead writer for the Ticker. Follow him on Twitter.)