Former Vice President Dick Cheney and his wife Lynne on Monday jumped into a bitter public clash between their two daughters over gay marriage, an anguished personal fight that reflects a broader debate within the Republican Party over allowing same-sex couples to marry.

The Cheneys defended their eldest daughter, Liz Cheney, a U.S. Senate candidate in Wyoming, who on Sunday reaffirmed her opposition to same-sex marriage. And they expressed dismay that their younger daughter, Mary Cheney, and her spouse chose to publicly express their anger about her stance.

“This is an issue we have dealt with privately for many years, and we are pained to see it become public,” Dick and Lynne Cheney said in a statement. “Since it has, one thing should be clear. Liz has always believed in the traditional definition of marriage.”

The public eruption of the internal Cheney family drama gave airing to the struggle within the GOP over gay marriage, which is rapidly gaining legal status and wider public acceptance.

Some influential party strategists and top GOP donors have rallied around efforts to legalize same-sex marriage, garnering support from the likes of Sen. Rob Portman, R-Ohio. Earlier this year, more than 100 Republicans signed a legal brief urging the Supreme Court to declare that gays and lesbians have a constitutional right to marry.

Public surveys show GOP attitudes about same-sex marriage are changing, albeit at a much slower pace than the overall population. In a March Post-ABC poll, 34 percent of Republicans said they believe it should be legal for gay and lesbian couples to marry, up from 22 percent in 2009. Among Republicans and GOP-leaning independents under 50 years old, the support for gay marriage was much higher, with 52 percent backing it.

“When you look at the question of same-sex marriage, there is a consistent trend that more and more people are becoming supportive of it,” particularly younger GOP voters, said Republican strategist Liz Mair, a member of the board of Young Conservatives for the Freedom to Marry. “That does tell you something about where the future of the issue is going and where candidates would be best positioned to be electorally on it.”

But gay marriage remains a deeply polarizing issue among social conservatives, who are key players in the party and exert strong sway in GOP primary elections. In Wyoming, a conservative super PAC called American Principles Fund ran a television ad for three weeks this fall noting that Cheney is opposed to a federal constitutional amendment banning gay marriage.

“This is a huge issue for Republican primary voters and it will carry over to the general election,” said the group’s executive director, Sarah Huckabee Sanders, who is the daughter of former Arkansas Governor Mike Huckabee. “Jobs and economy and spending are still the most important, but a candidate’s position on social issues such a life and marriage sends an extremely strong message about their values. That’s why taking the wrong side could be fatal.”

David Lane, an influential Christian activist based in California, said “the Republican Party will collapse if they bring homosexual marriage into the party.”

In Wyoming, where Cheney is taking on incumbent Sen. Mike Enzi, some party strategists doubted that the topic would be a deciding factor in the August 2014 primary, but noted the public spat threatened to overshadow other issues.

Bill Novotny, a veteran Republican strategist with ties to both candidates who is neutral in the race, said he saw the issue as “more of a distraction than a complication” since Cheney and Enzi have similar positions on same-sex marriage.

Cheney’s campaign is “losing valuable time trying to put this spat to rest when they should be articulating their reasons why Wyoming needs to give Mike Enzi a pink slip,” Novotny said.

The back-and-forth began Sunday when Liz Cheney appeared on “Fox News Sunday,” where she reiterated her opposition to same-sex marriage, telling host Chris Wallace that she holds a different view on the subject than her younger sister, Mary, who married her longtime partner Heather Poe in 2012.

“I love Mary very much. I love her family very much. This is just an issue on which we disagree,” Liz Cheney said.

That prompted an angry response from Poe, who wrote on Facebook : “Liz has been a guest in our home, has spent time and shared holidays with our children, and when Mary and I got married in 2012 — she didn’t hesitate to tell us how happy she was for us. To have her now say she doesn’t support our right to marry is offensive to say the least.”

Mary Cheney shared the message on her own Facebook page, adding: “Liz — this isn’t just an issue on which we disagree — you’re just wrong — and on the wrong side of history.”

She elaborated in a comment posted later Sunday afternoon that her sister’s position “is to treat my family as second class citizens.”

Their parents sought to referee the feud Monday, saying that Liz Cheney has “always treated her sister and her sister’s family with love and respect, exactly as she should have done.”

“Compassion is called for, even when there is disagreement about such a fundamental matter, and Liz’s many kindnesses shouldn’t be used to distort her position,” they said in their statement.

This is not the first time that the family has wrestled with the personal implications of the national debate over gay marriage. Mary Cheney considered quitting her position on George W. Bush’s reelection campaign in 2004 when he used his State of the Union address to defend “the sanctity of marriage,” according to “Days of Fire: Bush and Cheney in the White House,” a book by New York Times reporter Peter Baker.

Dick Cheney endorsed state-sanctioned gay marriage in 2009, saying in remarks at the National Press Club in Washington that “people ought to be free to enter into any kind of union they wish, any kind of arrangement they wish.” That same year, when she was asked on MSNBC what her stance was, Liz Cheney declined to answer directly, saying that she believed it was an issue that should be left to the states. “My family’s been very clear about this: We think freedom means freedom for everybody,” she said.

A spokeswoman for Liz Cheney did not respond to a request for comment Monday. Mary Cheney and Poe did not respond to a voicemail message left for them.

The high-profile spat underscores how much attitudes within the party have changed, in part because gay Republicans such as Mary Cheney are increasingly living their lives openly, activists said Monday.

“The fact that you have this discussion is because Mary Cheney lives her life honestly as a gay American,” said Gregory Angelo, executive director of the Log Cabin Republicans, a group that advocates for gay rights.

But, Angelo added, “I feel Liz did miss an opportunity, if she really did want to distinguish herself from Sen. Enzi, to position herself as a new generation Republican. It does show there is still work to be done, and that Republicans do not walk in lockstep.”