WASHINGTON (CNN) -- Former Massachusetts Gov. Mitt Romney described the practice of polygamy "awful," and said he understands that many people find this part of the Mormon religion's history "troubling," in an interview set to air Sunday on CBS's "60 Minutes."

"I have a great-great grandfather. They were trying to build a generation out there in the desert and so he took additional wives as he was told to do," Romney, a Mormon, said in the CBS interview. "And I must admit I can't imagine anything more awful than polygamy."

The Mormon Church outlawed the practice of polygamy in 1890.

In the interview, Romney, who is seeking the Republican presidential nomination, also faults the Bush administration with "a number of errors," in preparing for the aftermath of the Iraq war.

"I don't think we were adequately prepared for what occurred," he said. "I don't think we did enough planning. I don't think we considered the various downsides and risks."