Cheney, who is openly gay, is married to Heather Poe and now travels the nation supporting same-sex marriage.
Mary Cheney recently had a public clash over the issue with her sister, who is running to unseat Republican U.S. Sen. Mike Enzi of Wyoming. Liz Cheney reaffirmed last month that she opposes gay marriage.
Indiana lawmakers will take up the question next month of whether the state constitution should be amended to limit marriage to being between one man and one woman.
If approved, the amendment would face a statewide referendum in November 2014.
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