Rob Portman, Senator from Ohio, became the first sitting Republican member of the US Senate to openly support gay marriage. Portman's son came out of the closet two years ago. Portman announced his support for gay marriage, in part because of his realization that he wanted his son to be able to marry. Portman was one of the top candidates to be Mitt Romney's running mate. Portman, apparently, told Romney about his gay son during the vetting process. It, apparently, was not a secret in political circles about his gay son.
Portman announced his support in anticipation of people asking him about gay marriage with the upcoming Supreme Court case. Portman did not discuss about how he felt about the cases on the Supreme Court. He made it very clear that it was a personal decision. It is possible that he will come out in support of overturning Proposition 8 but has not said so at this time.