Former Vice President Dick Cheney waded into a public dispute between his daughters on Monday, highlighting the debate in the Republican party over same-sex marriage.

The dispute began when daughter Liz Cheney, who is running for a Wyoming Senate seat, said she would not change her position on same-sex marriage despite her sister Mary’s marriage to a woman, saying “I believe in the traditional definition of marriage.” Mary responded, saying her sister was “on the wrong side of history.”

Half the general public supports allowing gays and lesbians to marry legally, up 15 points from 35% in 2001. But just 29% of Republicans do. Although support among Republicans has been growing, up 8 points from 21% in 2001, it’s risen more slowly than in the general public. There is more support for gay marriage among liberal and moderate Republicans (42%) than among conservative Republicans (23%).

About half of Americans (49%) say they have a close family member or friend who is gay or lesbian, and Pew Research surveys find that knowing someone who is gay is associated with acceptance of gay marriage. For example, 14% of Americans said in a survey this past spring that they had changed their minds in favor of gay marriage. When asked why, 32% of those who had changed their minds said it was because they had friends, family or acquaintances who are gay or lesbian.

In a separate survey of LGBT Americans earlier this year, Pew Research found that 77% of lesbian and gay adults with sisters have told a sister about their sexual orientation or gender identity (75% of those with brothers have told a brother.) That’s comparable to the share who have told their mother about their sexual orientation or gender identity (among those who could have told their mother, 76% have), and significantly higher than the share who have told their father (among those who could have told their father, 63% have). The survey found that while for many LGBT adults discussing their sexuality with their parents was difficult, over the long run it did more to strengthen their relationship with their parents than to weaken their relationships.