Letterman Apologizes

Yet similar jokes never drew much objection from Palin's camp until Letterman's gag last week about Palin's daughter getting "knocked up" by baseball player Alex Rodriguez during a visit to a New York Yankees game -- a line Palin suggested was really a reference to her 14-year-old daughter, Willow, who attended the game.

On Sept. 2, during the presidential campaign, Leno, for example, told this joke on "The Tonight Show": "Governor Palin announced over the weekend that her 17-year-old unmarried daughter is five months pregnant. And you thought John Edwards was in trouble before! Now he has really done it."

On Oct. 10, O'Brien, then host of "Late Night," quipped: "Sarah Palin is going to drop the first puck at the Philadelphia Flyers hockey game. Then Palin will spend the rest of the game trying to keep the hockey players out of her daughter's penalty box."

Never fully disappeared
While the pregnant-daughter theme was most common on late-night shows during the fall campaign, it has never fully disappeared. And Letterman told far fewer of these jokes than some of his late-night brethren.

Through mid-March, Leno had made 15 jokes about the Palin daughter's pregnancy, Stewart had told four on "The Daily Show," and Letterman checked in with eight, according to an analysis of late-night humor by the Center for Media and Public Affairs, a nonpartisan research organization affiliated with George Mason University.

The comedian most likely to bash Bristol Palin? O'Brien, with 20 jokes at her expense.

"Saturday Night Live" has also parodied the Palin family in questionable ways. In a skit last September, a mock reporter joked about incest in the vice presidential candidate's family, saying, "I mean, come on. It's Alaska!"

Palin not only didn't protest, she appeared as a guest on the program a few weeks later.