Back in the mid-1990s, then-congressman Rob Portman led the effort to pass the Defense of Marriage Act, which defines marriage as between a man and a woman. It also bars the federal government from recognizing same-sex marriage.
But in 2011, Portman's son Will told him that he was gay, setting in motion a complete reversal.
"This is one of those issues I think a lot of us maybe don't focus on until a friend or a family member or someone else talks to us about it," said Portman. "That certainly had a big impact on me. From the perspective of a father, it became an issue I looked at differently."
In the weeks since Portman's announcement that he now supports same-sex marriage, he has received criticism from both the political right and left for changing his views.
Citizens for Community Values Pastoral Liaison Dr. Kent Spann said while he understands the issue has become personal for Portman, it shouldn't change his political opinion.
"The truth of the position is still that marriage should be between one man and one woman, and that doesn't have anything to do with whether you love your child or not," said Span.
Chris Long from Ohio's Christian Alliance told 10TV that candidates in the future, including Portman, will be held accountable for their position on marriage.
Portman said he understands the complaints, but new information can make you rethink some issues.
"I suspect that people who have colleagues or friends or family members who are gay who talk to them, in my case my son did talk to me about my positions on the issues, I think that can be very influential," Portman said.
Portman also dismisses complaints from the left that his views should have been shaped by tolerance and not by a family member.
"I was confronted with a personal situation, my son. That lead me to think about the issue much more deeply," said Portman. "I've been very frank about that."
Nearly 20 years ago, the "father" of the modern conservative movement Barry Goldwater, the 1964 GOP presidential nominee, warned Republicans they were on the wrong side of history in the gay rights movement.
"The big thing is to make this country, along with every other country in the world with a few exceptions, quit discriminating against people just because they're gay," said Goldwater in 1994. "It's time America realized that there is no gay exemption in the right to life, liberty, and the pursuit of happiness in the Declaration of Independence."
Portman made history last month becoming the first sitting Republican senator to endorse same sex marriage. Illinois Republican Sen. Mark Kirk announced his support on Tuesday.
"We have different points of view in our caucus on this obviously," Portman said. "I did not talk to Sen. Kirk about it before he made his decision. People have been very respectful and I've had a lot of good conversations about it."
Portman said the economy and the deficit remain his focus in Washington. But he does admit the topic of same sex marriage has come up as he traveled the state this past week.
"I don't think churches should not be required to perform weddings they don't approve of or recognize marriages they don't approve of, and that's something I've talked to a lot of Ohioans about this past week that I've been home," Portman said. "This is not about telling churches what they have to do. It's about letting individuals make that choice for themselves."
Portman smiles when talking about his son Will, who wrote an op-ed for the Yale newspaper last month about coming out.
"He's a great kid. I have a lot of respect for him," said Portman. "I hope he's studying, with those kind of tuitions - he'd better be."
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