NEW YORK ( CNN ) -- John McCain has learned his lesson : Do n't ever cancel on David Letterman . Appearing on CBS ' `` Late Show with David Letterman '' Thursday , the Republican presidential candidate apologized for skipping out on a scheduled visit in September that Letterman later made the subject of an ongoing joke . `` I screwed up , '' McCain told Letterman more than once in the interview that aired Thursday night . McCain 's appearance on the show comes three weeks after he raised the ire of the generally mild-mannered host by canceling at the last minute , citing his decision to suspend his presidential campaign because of the financial crisis . `` This does n't smell right , '' Letterman said . `` This is not the way a tested hero behaves . Somebody 's putting something in his Metamucil . '' Letterman also did n't appear to buy the Arizona senator 's explanation for the cancellation . At the time , he showed the audience a live feed of McCain preparing for an interview with CBS anchor Katie Couric . After praising McCain 's record as a prisoner of war in Vietnam , he said , `` This is not the John McCain I know , by God . '' Letterman has repeatedly harped on McCain for the missed appearance , noting the Arizona senator 's poll numbers appeared to begin to slide right after he skipped out on the show . `` Look at all the conversation I gave you . Including having Mr. Olbermann on , '' McCain told Letterman Thursday night , referencing the MSNBC liberal talk show host who filled in for him that night . However , Thursday 's interview was not all fun and games , as Letterman pressed McCain on Republican VP Sarah Palin 's preparedness to lead the country through `` the next 9/11 attack.. '' `` Absolutely , '' she is , McCain said . `` She has inspired Americans . That 's the thing we need . '' McCain said her experience as a mayor , governor and PTA member have prepared her to be president . `` In all due respect , one of the people I admired most was an obscure governor of a southern state called Arkansas and he turned out to be a fairly successful president , '' McCain said . `` I mean , Ronald Reagan was a cowboy , no experience in international affairs . So , look , I think she has shown leadership . '' When Letterman asked McCain about Palin 's charge that Barack Obama `` palled around with terrorists , '' the senator said `` he did . '' McCain said that while Obama might have been just a child when William Ayers founded the Weathermen , a Vietnam War era group blamed for several domestic bombings . Ayers recently said he regretted not doing more attacks . `` Mr. Ayers , on 2001 , September 11 , 2001 said , ' I wish I had bombed more , ' '' said McCain . McCain 's reference was to a New York Times story published on September 11 , 2001 , when Ayers wrote `` I do n't regret setting bombs ... I feel we did n't do enough . '' Later , after the issue was raised in an April primary debate by Sen. Hillary Clinton , Ayers posted his 2001 reply to the Times story on his blog , saying , `` I said I had a thousand regrets , but no regrets for opposing the war with every ounce of my strength . ''
`` I screwed up , '' John McCain tells David Letterman for canceling scheduled visit . Letterman used McCain 's no-show as subject of ongoing joke . Comment: