Thomas Peters of the National Organization for Marriage (NOM) on Friday criticized Ohio Senator Rob Portman's shift on gay marriage, saying the senator can say goodbye to his presidential aspirations.

Portman, a Republican, on Friday announced that he had reversed his stance on the issue, revealing that his son, Will Portman, had come out to him and his wife two years earlier. Portman is the first GOP senator to buck the party's official stance.

In an op-ed and later in a sit-down with CNN, Portman added that he was not prepared to advocate on the issue. A critical point, considering marriage equality advocates are working to repeal Ohio's amendment defining marriage as a heterosexual union.

(Related: Senator Rob Portman reverses course on gay marriage.)

Speaking with, Peters argued that Portman could lose his seat over the issue.

“What Mr. Portman is doing is shrinking the size of the GOP tent,” Peters said from CPAC. “I think it will have huge consequences if he chooses to run again.”

“As far as Senator Portman and presidential chances, I think he can say goodbye to those,” Peters added.