Yet humor does have its limits. Some politicians have asked Parvin for joke material to defuse serious trouble. "If you're about to be indicted, that's too far a reach," he says. "I tell them no, it is serious, you need to be serious about it."
War, as President Bush learned, is also best avoided. At the White House Correspondents Dinner in May 2004, he appeared in a video searching under furniture in the Oval Office.
"Those weapons of mass destruction have got to be somewhere," he said. Although the dinner is a traditional showcase for presidential humor, there was scathing backlash from Democrats, anti-war liberals and relatives of servicemembers. They said it was disgraceful that Bush was making light of a decision to go to war.
Off-the-cuff jokes are another risky move but can be valuable for both candidate and voter. "Spontaneous humor gives a speaker the ability to connect with his audience. It makes that person seem human and likable," Keller says.
Former New York mayor Rudy Giuliani pulled that off at a CNN debate last month when microphone problems interrupted his answer to a question about his differences with Catholic bishops. Told lightning was the culprit, he laughed and said: "For someone who went to parochial schools his whole life, this is a very frightening thing."
McCain has been criticized by fellow Republicans for backing a plan to allow millions of illegal immigrants to become citizens. When his rivals attacked his stance at the CNN debate, he broke up the audience by saying, "Muchas gracias."
In the Democratic debate Monday featuring video submissions from YouTube users, the questions and the candidates were edgier than usual. Edwards, asked to name something he doesn't like about Clinton, stared at the brightly colored jacket she was wearing: "I'm not sure about that coat."
And Biden, asked to say what he liked about Ohio Rep. Dennis Kucinich, replied: "Dennis, the thing I like best about you is your wife." Elizabeth Kucinich is tall, red-haired, British and 31 years younger than her 60-year-old husband.
In January, Clinton discovered the unintended consequences of spontaneity when she rephrased a question as "what in my background equips me to deal with evil and bad men?" and then grinned. Her listeners in Davenport, Iowa, laughed for 30 seconds; many assumed it was an allusion to her unfaithful husband.
Not so, she told reporters later: "You guys keep telling me lighten up, be funny. So I get a little funny, and now I'm being psychoanalyzed."
Katz says that in his view she was not referring to Bill Clinton, but adds: "The joke didn't work on its own terms because it accessed the wrong synapses in your brain. That's the risk-reward ratio."
One way to take control of humor is to make funny ads and videos. New Mexico Gov. Bill Richardson has moved up to double-digits in Iowa polls since starting a series of ads called "Job Interview." Each is a skit with a crass interviewer and the bemused governor.
In one, the interviewer reviews the Democrat's résumé— congressman, U.S. energy secretary, United Nations ambassador, Nobel Peace Prize nominee — and chews food as he asks, "So, what makes you think you can be president?"
"The public likes politicians to bring themselves down a notch," Richardson says. "Everyone's gone through a job interview. Everybody's been interviewed by some jerk who doesn't think you're very good. People can relate to that."