03/19/2013 11:20 am ET Updated Feb 02, 2016

Clinton, Portman for Marriage Equality: Can Momentum Sway the Court?

Socially conservative Sen. Rob Portman's dramatic announcement last week that he supports same-sex marriage -- a switch motivated by learning, two years ago, that his son is gay -- is once again proof of what is working in favor of the LGBT movement: timing and tone.

The timing is really fortunate, coming less than two weeks before the Supreme Court will take up the constitutionality of Proposition 8, California's ban on same-sex marriage, and the Defense of Marriage Act, which limits the federal benefits to gay couples. Hillary Clinton's announcement on Monday that she supports same-sex marriage only adds to the "bandwagon effect," or the idea that marriage equality is no longer a matter of if, but when.

"There is no question where this country is headed on marriage equality and it is headed there fast," Human Rights Campaign president Chad Griffin said Friday on MSNBC's Andrea Mitchell Reports. Marriage equality activists are by no means assured that the Supreme Court will decide in their favor, or even decide at all.

Clinton's announcement was meant to inspire, but it was not a surprise. Portman's was. His announcement in and of itself may not immediately sway others in his party, it only adds to the perception and perhaps even demographic reality of inevitability.

The partisan composition of the court has not changed since the Prop 8 suit was filed, almost four years ago, but public opinion has. This is where organizations like Freedom to Marry, the American Foundation for Equal Rights, the Human Rights Campaign and other groups have been so successful, illuminating this shift in the spectrum of amicus briefs filed in the cases and in the publicity leading up to the arguments. If there's worry among the justices in getting ahead of history, or of creating another Roe v. Wade era of polarization, the messaging on the side of marriage equality is that a bipartisan consensus is building. In other words, there is safety in knowing where it is headed.

According to a spokesman for HRC, Portman's announcement was not coordinated with their group, or any other that he knew of. The upcoming oral arguments were part of his decision to announce his new position.

"I thought it was the right time to let folks know where I stand so there's no confusion, so I would be clear about it," he told CNN's Dana Bash.

Nevertheless, what's not getting talked about as much as his switch is that he's not keen on the idea of judicial intervention, and argues that it should be left to the states. "An expansive court ruling would run the risk of deepening divisions rather than resolving them," he wrote in an op-ed in the Columbus Post Dispatch. In fact, the most powerful argument that supporters of Prop 8 probably have before the court is that it is merely the will of the people.

The court cases, and the public campaigns around them, as well as a cultural shift toward Modern Family and The New Normal, undoubtedly have helped blur the partisan boundaries around marriage equality.

That may be the dividend of the legal battle, no matter how the court decides. Portman's op-ed stirred criticism in social media, where commentators have chided him for switching sides only when it hit home and got personal, but he wasn't speaking to that audience, but to the "family values" social conservatives like himself.

"Ultimately, it came down to the Bible's overarching themes of love and compassion and my belief that we are all children of God," he wrote, framing it on the same religious terms that those who want to keep marriage between a man and a woman. He may not have changed minds, but he's helped give new dimension to the debate.