The family of former vice-president, Dick Cheney, are realising politics and family are not always compatible as they battle over gay marriage.

First some history...

Cheney's daughter, Liz, is running for Republican Senate primary in Wyoming, a typically conservative state requiring a senator with suitably conservative views.

dick cheney liz mary

Liz and Mary pictured in 2004

The other Cheney daughter, Mary, is a married lesbian with two children.

So Mary's partner, Heather Poe was understandably upset over the weekend when Liz set out her opposition to gay marriage in an interview with Fox News.

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

Heather took to Facebook to note her dismay.

She wrote:

I was watching my sister-in-law on Fox News Sunday (yes Liz, in 15 states and the District of Columbia you are my sister-in-law) and was very disappointed to hear her say "I do believe in the traditional definition of marriage."

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.

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.

I always thought freedom meant freedom for EVERYONE.

Mary then also stepped in and said: "Liz - this isn't just an issue on which we disagree - you're just wrong - and on the wrong side of history."

Adding to the family tension is Dick's stance on the issue.

He endorsed state-sanctioned gay marriage in 2009 but is backing Liz's campaign - and therefore her views.