(CNN) -- Republicans on Sunday described cracks appearing in their party's long-held opposition to same-sex marriage, an issue set to gain renewed attention when the Supreme Court hears arguments on its legality this week.
"There is no putting this genie back in the bottle. It is undeniable. The shift is here and we're not going back." Republican strategist and CNN contributor Ana Navarro told CNN chief political correspondent Candy Crowley on "State of the Union."
That shift was evident this week when Sen. Rob Portman, a Republican from Ohio, endorsed same-sex marriage. Portman, who was considered a top potential running mate for Mitt Romney in last year's election, said his decision was influenced by his son, who is gay.
"I've come to the conclusion that for me, personally, I think this is something that we should allow people to do, to get married, and to have the joy and stability of marriage that I've had for over 26 years," Portman told CNN chief congressional correspondent Dana Bash.
Portman was the first Republican in the U.S. Senate to come out in support of same-sex marriage, but other Republicans aren't far behind, predicted veteran Republican strategist Karl Rove.
Asked if he could foresee a Republican presidential candidate in 2016 supporting same-sex marriage, Rove said Sunday, "I could." He was speaking on ABC's "This Week."
One of those potential candidates, Sen. Rand Paul of Kentucky, reiterated his belief Sunday in "traditional marriage" between a man and a woman. But he said a federal ban like the Defense of Marriage Act, known as DOMA, isn't necessary, since states should be determining their own marriage laws.
"I don't want the government promoting something I don't believe in," he said on "Fox News Sunday." "But I also don't mind if the government tries to be neutral on the issue."
The high court will hear two appeals this week pertaining to same-sex marriage -- the first involving DOMA, the federal law signed in 1996 that defines marriage as between one man and one woman.
The second case involves California's Proposition 8, a 2008 referendum that abolished same-sex marriage after the state's highest court ruled it legal.
Polls have shown support for same-sex marriage steadily rising in the U.S., with gaps persisting between older and younger Americans. The shift has also played out among national figures who have changed their positions on the issue, including some notable Democrats: President Barack Obama, former President Bill Clinton, and former Secretary of State Hillary Clinton, who announced for the first time last week that she supports same-sex marriage.
Republicans, Navarro argued Sunday, were moving in the same direction.
"I do feel an evolution and a shift, a small change, albeit, in the Republican Party," she said. "People who maybe a few years ago were saying, 'Hell, no, we won't go there,' are now saying it should be states' rights. They are talking about it in a different way. The people who are talking in a very strident way are now a minority."
Tony Perkins, the president of the socially conservative Family Research Council, argued the opposite Sunday, saying there was no indication Americans were moving toward supporting same-sex marriage.
"The reality is it's not inevitable," Perkins said on CBS's "Face the Nation." "And the American people, as they've had the opportunity to speak on this, have spoken overwhelmingly. Thirty states, eight additional states, have the definition of natural marriage into their statutes. So we're far from being at a point where America has embraced same-sex marriage."