"I screwed up. What can I say?" the Republican presidential nominee told Letterman on Thursday night's show.
There was, however, a silver lining, said McCain.
"Look at all the conversation I gave you," he told Letterman.
The late-night host had been skewering the Arizona senator since he missed a Sept. 24 appearance during the momentary suspension of his campaign due to the economic crisis.
"You called me an hour and a half [before showtime] and said, 'We've got to get right back to Washington,'" complained Letterman. "But you didn't go right back to Washington!"
Instead on that day, McCain sat for an interview in New York with Katie Couric.
Pressed on PalinAt times, McCain appeared to have been placed on a hot seat. In several questions, Letterman pressed the candidate about his choice of running mate.
"In your guts, in your stomach," asked Letterman, who said he has no political-party affiliation, "if I were to run upstairs and wake you in the middle of the night and say, 'John, is Sarah Palin really the woman to lead us through the next four, eight years – through the next 9/11 attack?' "
Replied McCain: "Absolutely. She has inspired Americans. That's the thing we need."
Asked if he backs Palin's claim on the campaign trail that Democratic candidate Barack Obama "palled around with terrorists," McCain said his rival needs to better explain his relationship with former Weather Underground activist William Ayers.
"Did you not have a relationship with Gordon Liddy?" Letterman inquired.
McCain acknowledged knowing the Watergate burglar. Following the commercial break, McCain further said, "I know Gordon Liddy. He paid his debt, he went to prison ... I'm not in any way embarrassed to know Gordon Liddy."
"You understand the same case could be made of your relationship with him as is being made with William Ayers?" Letterman said.
McCain responded that he has been completely open about his relationship with Liddy.
As if not accepting the implication that Obama and Ayers had a relationship – Obama was 8 when Ayers was 29, the TV host noted – Letterman asked McCain, "Are they double-dating, are they going to dinner, what are they doing? Are they driving across country?"
"Maybe going to Denny's," McCain replied.
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