Sen. Rob Portman of Ohio made headlines last night when CNN posted an interview in which he acknowledged his support for same-sex marriage, a decision he made when he learned his son, Will, a junior at Yale, is gay (for what it’s worth, Will tweeted this morning that he’s “especially proud” of his dad).

Portman published an op-ed in the Columbus Dispatch, where he referenced his Christian faith twice (he’s Methodist):

At the time, my position on marriage for same-sex couples was rooted in my faith tradition that marriage is a sacred bond between a man and a woman. Knowing that my son is gay prompted me to consider the issue from another perspective: that of a dad who wants all three of his kids to lead happy, meaningful lives with the people they love, a blessing Jane and I have shared for 26 years.

I wrestled with how to reconcile my Christian faith with my desire for Will to have the same opportunities to pursue happiness and fulfillment as his brother and sister. Ultimately, it came down to the Bible’s overarching themes of love and compassion and my belief that we are all children of God.

Is Portman’s newfound support for marriage equality a watershed moment in the debate over marriage equality? It was inconceivable just a few years ago that anyone who supported same-sex marriage would be eligible for the presidency. Today, no Democrat will be nominated if she or he isn’t on board with the idea. Is the GOP next?

NBC reporter Kasie Hunt tweeted this morning that the Romney campaign was aware of Portman’s son’s sexuality but that it had no role in choosing Ryan over the Ohio Republican. One wonders, given Romney’s pitifully low levels of support from those supporting same-sex marriage, if choosing Portman, and making this revelation sooner, would have helped his chances at the White House.

Some on the left accuse Portman of hypocrisy or of being disingenuous, supporting same-sex marriage only because the issue now affects his family directly. Perhaps they forget that it’s well known that all people, especially people of faith, begin to come around on LGBT issues when they know someone personally who is open and out about their sexuality. So Portman’s change of heart after learning about his son isn’t a surprise and it’s not something to deride.

Finally, Portman’s marriage announcement is a good opportunity to remember that being against marriage equality is quickly becoming a belief that is outside the mainstream, including–no, especially for–people of faith.