The New York Times addresses this "problem":

Comedy has been no easier for the phalanx of late-night television hosts who depend on skewering political leaders for a healthy quotient of their nightly monologues. Jay Leno, David Letterman, Conan O’Brien and others have delivered a nightly stream of jokes about the Republican running for president — each one a variant on the same theme: John McCain is old.

But there has been little humor about Mr. Obama: about his age, his speaking ability, his intelligence, his family, his physique. And within a late-night landscape dominated by white hosts, white writers, and overwhelmingly white audiences, there has been almost none about his race.

“We’re doing jokes about people in his orbit, not really about him,” said Mike Sweeney, the head writer for Mr. O’Brien on “Late Night.” The jokes will come, representatives of the late-night shows said, when Mr. Obama does or says something that defines him — in comedy terms.

“We’re carrion birds,” said Jon Stewart, host of “The Daily Show” on the Comedy Central channel. “We’re sitting up there saying ‘Does he seem weak? Is he dehydrated yet? Let’s attack.’ ”

But so far, no true punch lines have landed.

Why? The reason cited by most of those involved in the shows is that a fundamental factor is so far missing in Mr. Obama: There is no comedic “take” on him, nothing easy to turn to for an easy laugh, like allegations of Bill Clinton’s womanizing, or President Bush’s goofy bumbling or Al Gore’s robotic persona.

This is probably true, now that I think of it.

Fortunately, Andy Borowitz got a hold of five jokes from the Obama campaign:

Obama Releases List of Approved Jokes About Himself

Bid to Help Late Night Comics

Saying he is "sympathetic to late night comedians’ struggle to find jokes to make about me," Sen. Barack Obama (D-Ill) today issued a list of official campaign-approved Barack Obama jokes.

The five jokes, which Sen. Obama said he is making available to all comedians free of charge, are as follows:

Barack Obama and a kangaroo pull up to a gas station. The gas station attendant takes one look at the kangaroo and says, "You know, we don’t get many kangaroos here." Barack Obama replies, "At these prices, I’m not surprised. That’s why we need to reduce our dependence on foreign oil."

A traveling salesman knocks on the door of a farmhouse, and much to his surprise, Barack Obama answers the door. The salesman says, "I was expecting the farmer’s daughter." Barack Obama replies, "She’s not here. The farm was foreclosed on because of subprime loans that are making a mockery of the American Dream."

A horse walks into a bar. The bartender says, "Why the long face?" Barack Obama replies, "His jockey just lost his health insurance, which should be the right of all Americans."

Q: What’s black and white and red all over?
Barack Obama: The New Yorker magazine, which should be embarrassed after publishing such a tasteless and offensive cover, which I reject and denounce.

A Christian, a Jew and Barack Obama are in a rowboat in the middle of the ocean. Barack Obama says, "This joke isn’t going to work because there’s no Muslim in this boat."