MANCHESTER, N.H.—When John McCain joined Mitt Romney on the campaign trail this week, he brought with him something unfamiliar in this year’s race: laughter. Following former New Hampshire Gov. John Sununu at a rally on Wednesday, McCain said it reminded him of his favorite joke about governors: “There were two inmates in the chow line in the state prison and one of them turned to the other and said the food was a lot better in here when you were governor.”

A remarkable fact about the 2012 Republican presidential campaign is that it is not funny. Republican candidates give speech after speech and draw only a handful of chuckles, and the occasional wry smile. This makes for boring politics, but it also makes for bad politics. People want to like politicians they vote for and a smile helps with that. Laughter is also an effective tool for undermining your opponents and spreading your message with voters.

You would be on firm ground if you said that times are too serious for a lot of jokes. You would also be on boring ground, and we would quickly move away from you and find someone more pleasant to talk to. It is possible to be humorous and serious at the same time. Great presidents who faced trying times were known for their humor. FDR mocked his Republican opponents in his “Fala speech,” which got its name from his charge that his opponents would stoop to even attacking his dog: “I don’t resent attacks, and my family doesn’t resent attacks, but Fala does resent them.” Abe Lincoln’s wit was collected in volumes Old Abe’s Jokes and Abe’s Jokes—Fresh From Abraham’s Bosom, John Kennedy was a first-class wit, and Ronald Reagan was a famous jokester. “I hope you’re all Republicans,” he quipped before doctors operated on him after the 1981 assassination attempt.

Herman Cain is the only candidate who consistently drew a laugh. (This is not strictly true, I suppose: The others have generated their share of laughs—Rick Perry has been hysterical—but rarely intentionally.)

This is a once-in-a-generation political humor crisis. Every campaign since 1968 has had at least one candidate who could make audiences smile. In 2008, Gov. Mike Huckabee and McCain could have qualified for Last Comic Standing. Even grimmer candidates such as Bob Dole and Pat Buchanan cracked jokes. My favorite from Dole, who wrote a book on political wit: “History buffs probably noted the reunion at a Washington party a few weeks ago of three ex-presidents: Carter, Ford and Nixon—See No Evil, Hear No Evil and Evil.” Although my all-time favorite use of comedy in a political campaign was this 1968 Hubert Humphrey ad in which the notion of Spiro Agnew as vice president sends a man off the deep end.

All of the Republican contenders insist they are optimists, but they don’t seem to realize that there is no better way to convey optimism than with a smile. Humor suggests that no matter how dark things are, you have the sensibility to laugh, to see a bit of sun around the corner. This is McCain’s gift. He certainly has no trouble conveying his fears—campaigning with Romney this week he spoke in dire terms about the danger the current president presents to American foreign policy—but his jokes suggest a brighter day.

Humor is particularly helpful if you’re trying to contrast yourself with a struggling incumbent. A sour sermon of despair can’t possibly leave voters at a town hall with a warm feeling.

There’s a social networking benefit to humor too. A joke well-told gives the audience something they can pass along later to their friends. It magnifies your message easily or at least makes voters feel good enough that they report back favorably about their experience at your rally. Harry Truman’s 1948 campaign—and arguably his presidency—was defined in a joke. During a speech attacking Republicans during that campaign, a supporter yelled “Give ‘em Hell, Harry!” Truman replied, “I don’t give them Hell. I just tell the truth about them and they think it’s Hell.” That quip became Truman’s nickname.

At the most recent debate Rick Santorum did show a little of this agility. While Ron Paul was attacking him the bell went off. When Paul paused Santorum interjected: “It caught you not telling the truth, Ron.”

Wit suggests an agile mind, which is useful for a president who needs to cut through complex subjects, rally people to a cause, or break the tension in negotiations. Given the polarization in Washington at the moment, perhaps wit is required more than ever. Peggy Noonan tells the story about Reagan, who listened while a reluctant senator explained why he wasn’t supporting a bill. “I’d jump out of a plane for you,” said the senator, testifying to his loyalty. Reagan responded, “Jump.” He got the vote. Among this year’s stock answers when Republican candidates are asked about bipartisanship and compromise is to cite Ronald Reagan’s cooperation with Democratic House Speaker Tip O’Neill. Their relationship was founded in part on joke telling.

And here’s a little tip for the candidates: It’s actually not that hard to tell jokes. You can just steal from Rep. Mo Udall. That’s what John McCain and Lamar Alexander did. “I’m Mo Udall and I’m running for president,” the failed Democratic candidate said, walking into a shop. “Yeah,” replied the barber, “we were just laughing about that.” (Though candidates repeat Udall’s best lines at their peril, like his observation that the difference between a cactus and a caucus is that with a cactus, the pricks are on the outside.)

You can go too far, of course. James Garfield’s political adviser warned him against humor—“Never make the people laugh. If you would succeed in life you must be solemn, solemn as an ass.” Herman Cain used humor so much to dodge questions that it was unsettling. That joke about not knowing the name of foreign leaders isn’t that funny if polls consistently show that voters think you’re incapable of handling a foreign policy crisis or managing the serious duties of the Oval Office.

My characterization of the current field may be slightly unfair to Newt Gingrich, who has been known to offer some humor. At a rally in Wolfeboro he signed a photograph from a voter named “Slim,” then said, “Nobody has ever called me slim.” At the last debate he said he was struggling to hold his tongue so as not to appear “zany,” a wry reference to a dig by Mitt Romney. But Gingrich is so busy calling people stupid and adopts such a lecturing tone it may be harder to hear the humor in his pitch. And the bile in some of his jokes may sap their effectiveness. When he said Michelle Bachmann was “factually challenged” and compared her to one of his dumb students, it may have struck some as funny, but it might also have just seemed mean.

It would be easier to endure the absence of laughter if the campaigns weren’t otherwise so silly. It’s not just that the debates and interviews force candidates into contortions. It’s also that the candidates spend much of their time engaging in ridiculous hyperbole, offering straw man arguments, and pandering outrageously. If there’s going to be clownish behavior, at least voters should get a few laughs out of it.