Vice President Dick Cheney decided to speak out after learning that President Barack Obama might open prosecutions of former Bush Administration officials, his daughter disclosed Thursday.

Elizabeth Cheney told Fox News’ Sean Hannity that her father decided to speak out after he learned there was a possibility of legal action.

“He certainly did not plan when he left office to be doing this,” Cheney’s daughter said. “But I think as we watched in those very first days and weeks after President Obama came into office when he released the memos that lay out for the terrorists — the techniques we used to question them. Then when he suggested in the Oval Office itself that he would be open to the prosecution of former Bush administration officials including many who weren’t political appointees potentially, you know really, I think, made my dad realize this was just fundamentally wrong. We had to speak out.”

Hannity said he was “impressed” by Cheney’s performance.

“One of the things that really impressed me today is I thought your dad was like a prosecuting attorney and just laying out a strong case, piece by piece by piece,” Hannity quipped. “But he very vividly outlined what we have now forgotten, because we’ve been safe for 7 1/2 years, and that is the attacks on 9/11.”

Cheney’s daughter accused President Obama of having a “September 10 mentality” and said she’d been thanked by a family member of a 9/11 victim following her father’s address.

“I think that when you read the president’s speech… he has a September 10 mentality,” Elizabeth Cheney said. “And one of the most moving messages I got today out of the many hundreds that i received was from a family member of a 9/11 victim, saying, ‘Thank you for reminding the country. Thank you for reminding the White House.’

“You know, this wasn’t a mess, as President Obama described it,” she continued. “This was an attack on the homeland.”

This video is from Fox’s Hannity, broadcast May 21, 2009.