proudest moment in his career, Late Show writer Bill Scheft boasted at
a Friday comedy writer panel held at Washington, DC's Newseum, was when
he got David Letterman to try to undermine guest John McCain's Bill
Ayers talking point by raising McCain's relationship with G. Gordon
Liddy - as if a political dirty trickster were the equivalent of a
terrorist involved with bombings which killed people, could have killed
hundreds more if his attempts worked and remains unrepentant. At the
event, organized by the Writers Guild of America, East, and shown
Saturday night on C-SPAN, Scheft declared of his effort to discredit an
anti-Obama point: "I'm more proud of that than any single joke that
I've written." That earned applause from the audience.
Later, to a chorus of "yeah" from other writers on the stage representing The Daily Show, The Colbert Report, Late Night, as well as another Late Show writer (Tom Ruprecht, who is in front of Scheft in the screen shot to be added to this CyberAlert), Scheft insisted the only reason the comedy shows don't make fun of President Barack Obama is because he's "a little too damn competent and we ain't used to that."
Earlier in the day, some of the participants delivered stand-up acts and DCRTV.com's "page 2" recounted this "joke" from Scheft: "Former Vice-President Dick Cheney - I actually don't have a joke here, I just like to say former Vice-President Dick Cheney." See: www.dcrtv.com 
[This item, by the MRC's Brent Baker, was posted Sunday afternoon on the MRC's blog, NewsBusters.org: newsbusters.org  ]
Scheft, a writer for Letterman since 1991, at the May 8 event:
The moment that I am most proud of having been on the show is when we had John McCain on after, you know, he, you know, bolted on us to go save the economy. When he came back to the show, and he was, at the time he was out on the campaign trail beating the Bill Ayers drone. And I gave Dave a note before we went on about McCain's relationship to Gordon Liddy. And, in the middle of the interview, McCain starts talking about Obama palling around with terrorists and Bill Ayers.
And I stand under the spiral staircase on stage and I was just standing there going: "Liddy, Liddy, say Liddy, please say Liddy, please say Liddy." And Dave said, "Well don't you have a relationship with G. Gordon Liddy?" And you just saw, you know, whatever chip was left in McCain's head just kind of, phhh, and "well I, you know, I know him." "Well, didn't you go to a fundraiser, didn't you attend a fundraiser at his house?" "Well I." "We'll be right back." Which is the great thing that a host can do, you know, "we'll be right back."...I'm more proud of that than any single joke that I've written." [Applause]
It's not because he's black and it's not because we're afraid. It's just that he's, just so far, just a little too damn competent and we ain't used to that. [multiple panelists say "yeah."]
Letterman's hit on McCain about Liddy comes a little past the 19-minute mark in the video linked on this page (ACT 3, Senator John McCain, Watch now) of the contentious interview on the October 16 Late Show: lateshow.cbs.com 
Scheft's bio on his site: www.billscheft.com