Here's a preview of John McCain on Late Show tonight. He told host David Letterman, "I screwed up," then laughed and did a little "gee whiz" shrug, and made an awkward joke about being tortured in Vietnam. "What can I say?!" the Republican presidential nominee asked. Um, maybe give a reason why you lied about having to fly back to DC when you bailed on Letterman's show last time? Apparently that wasn't in the cards. Letterman later hit McCain for paling around with Watergate burglar and would-be firebomber G. Gordon Liddy, even though McCain has slammed Barack Obama for an arguably more distant relationship with 1960s radical William Ayers. By the end of the segment McCain appeared to be in full retreat on the Ayers issue. Witness McCain statement at the end of the clip after the jump (along with more bizarre face-pulls).