WATCH: Do Rob Portman's Pro-Gay Politics Make Him Unelectable?

Rob Portman has admitted that his position on marriage equality would make it difficult to win a Republican presidential primary.

The Ohio politician, who last year became the first U.S. Senate Republican to endorse same-sex marriage, after his son came out to him, spoke openly about how his stance puts him "at odds with my party" in a recent interview with WSJ Live's Uncommon Knowledge.

"It's a reversal of my previous position, and it puts me at odds with my party in many respects," Portman told host Peter Robinson. "I believe it's a conservative. I came to it because my son came to me and said, to my surprise and my wife's surprise, that he was gay. We had a conversation for about a year about it."

"After considering what he told me and talking to a lot of folks who are involved with this issue, I was never, frankly, involved in it, and maybe I should've been, but I never really thought deeply about it," he continued. "It seems to me to the extent that it's not a choice, which is what I believe. That is, Republicans ought to treat people as they are."

Portman reasoned that allowing same-sex marriage is actually aligned with the values of the Republican Party, calling it "the right conservative position in terms of individual liberty and in terms of stronger families and in terms of treating people as they are." However, he recognized the difficulty holding such a stance would have in a presidential bid.

"It probably makes it difficult for me to win a primary election at the national level," he concluded.

Watch the video, in which Portman begins talking about same-sex marriage at 36:15, below.