WASHINGTON » They were the towheaded sisters who tagged along on campaigns, polite and smiling, as their father rose through Wyoming and then Washington politics to become one of the most powerful men in the country.

"We were as close as sisters can be," recalled Mary Cheney of her relationship with her older sister Liz.

But now, a feud between the two has spilled into public view, involving social media, an angry same-sex spouse, a high-profile election and a father who feels uncomfortably caught between his two children.

The situation has deteriorated so much that the two sisters have not spoken since the summer and the whole fuss threatens to get in the way of something former Vice President Dick Cheney desperately wants – a U.S. Senate seat for Liz.

Things erupted Sunday when Mary Cheney, a lesbian, and her wife were at home watching Fox News Sunday – their usual weekend ritual. Liz Cheney appeared on the show and said that she opposed same-sex marriage, describing it as "just an area where we disagree," referring to her sister. Taken aback and hurt, Mary Cheney took to her Facebook page to blast back: "Liz – this isn’t just an issue on which we disagree you’re just wrong – and on the wrong side of history."

But then Mary Cheney’s wife, Heather Poe, went further, touching on Liz Cheney’s relocation from northern Virginia to Wyoming to seek office. (Liz Cheney is already battling accusations of carpetbagging in the race.)

"I can’t help but wonder how Liz would feel if as she moved from state to state, she discovered that her family was protected in one but not the other," Poe wrote on her Facebook page. "Yes, Liz," she added, "in fifteen states and the District of Columbia you are my sister-in-law."

The feud reveals tensions not just within the family but in the Republican Party more broadly as it seeks to respond to both a changing America and an energized, fervently conservative base.

Indeed, while Liz Cheney seeks to make clear her opposition to same-sex marriage, her father more than a decade ago was able to embrace fairly moderate views on the subject, breaking publicly with President George W. Bush over Bush’s support for a constitutional amendment to ban same-sex marriage. He has gone further still since then, telling Barbara Walters in 2011, "I certainly don’t have any problem with" same-sex marriage.

But Liz Cheney, in her bid to defeat Republican Sen. Michael B. Enzi of Wyoming, is running to his right and seeking to capture conservatives and Tea Party enthusiasts.

Liz Cheney on Sunday declined to directly address the remarks from her sister and sister-in-law, but said in an email: "I love my sister and her family and have always tried to be compassionate towards them. I believe that is the Christian way to behave."

People who have spoken to Liz Cheney say she is irritated that her sister is making their dispute public and believes it is hypocritical for Mary Cheney to take such a hard-line now, given that she worked for the re-election of Bush, an opponent of same-sex marriage.

The relationship between the two sisters used to be quite different. The daughters drew especially close when their father ran as Bush’s running mate in 2000 and eventually became a figure of great controversy and enormous power as vice president. After their father left office in 2009, politically bruised and physically ailing, the sisters, who lived 15 minutes apart in Washington’s tony northern Virginia suburbs, would join their parents for a standing Sunday dinner at Liz’s house in McLean each week, along with their families, including Poe.

Mary Cheney, 44, said in a phone interview Sunday that she presumed her sister shared her father’s views on marriage, and that view was reinforced because Liz Cheney "was always very supportive" of her relationship with Poe and the couple’s two children. She learned otherwise in August when Liz Cheney declared, shortly after announcing her Senate candidacy, that she was opposed to gay nuptials. Mary Cheney said it is now "impossible" for the sisters to reconcile as long as Liz Cheney maintains that position.

"What amazes me is that she says she’s running to be a new generation of leader," Mary Cheney said, citing her 47-year-old sister’s slogan in her campaign against Enzi, 69. "I’m not sure how sticking to the positions of the last 20 or 30 years is the best way to do that."

Mary Cheney said it was her wife’s idea for the couple to take to Facebook to respond to Liz’s televised remarks. Poe seemed especially hurt that her sister-in-law had acted so embracing toward them in private, and then took this public position.

"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," Poe wrote. "To have her say she doesn’t support our right to marry is offensive to say the least."

In the interview, Mary Cheney, who is a longtime political consultant, said she would continue to raise the matter. Reminded by a reporter that such criticism could complicate her sister’s Senate campaign, Mary Cheney offered a clipped answer reminiscent of her father’s terse style. "OK," she said, before letting silence fill the air.

It is not the substance of the issue that could hurt Liz Cheney in Wyoming – her opponent also opposes same-sex marriage. But the ugly family drama and questions about what Liz Cheney truly believes could reinforce questions about her authenticity in a place where many voters have met their politicians in person and are already skeptical of an outsider like Liz Cheney, who was raised primarily in the suburbs of Washington.

Wyoming, a sprawling but sparsely populated state, has rarely seen such high-profile primaries, and this one has already experienced an ugly Cheney family episode: After former Wyoming Sen. Alan Simpson, a longtime friend of the family who served with Dick Cheney in the state’s congressional delegation, fretted to The this summer about how Liz Cheney’s challenge of Enzi would be divisive among the state’s Republicans, Lynne Cheney, the sisters’ mother and Dick Cheney’s wife, confronted him at a charity event and told him to "just shut up" – three times, Simpson claimed. When Lynne Cheney later said that the exchange never happened, Simpson called her denial "a damn baldfaced lie."

The former vice president is active and visible in his daughter’s Senate bid and this Wednesday, he will join her in Denver for a fundraiser to benefit her campaign. Early polls show Liz Cheney trailing Enzi, but her fundraising since declaring her candidacy has been robust.

As for Mary Cheney, she said that when she gets together with her parents these days, they know which subjects not to bring up.

"They come over for dinner and we don’t talk about Liz or the race," she said. "There is so much more to talk about."

The Cheneys have tried to be "as neutral as they can," added Mary Cheney. "My parents are stuck in an awful position."

As for the coming holidays, Mary Cheney said that her parents will come to her and Poe’s northern Virginia home for Thanksgiving and that she assumed her older sister would be in Wyoming.

At Christmas, the whole Cheney clan will head to the Jackson Hole area in Wyoming, where Liz Cheney now lives. But Mary Cheney said of her sister, "I will not be seeing her."

© 2013 The New York Times Company