As a voter, David Letterman apparently has little use for Mitt Romney. But as a late-night comic, Letterman can’t get enough of him.

“Mitt Romney looks like a guy modeling briefs on a package of underwear,” he joked recently on CBS’s Late Show with David Letterman. “He looks like a guy who goes to the restroom when the check comes...He looks like a guy who would run a seminar on condo flipping … He looks like that guy on the golf course in the Levitra commercial.”

If Letterman can’t stop ridiculing the Republican presidential nominee—who’s running neck and neck with President Obama a week before the Nov. 6 election—he’s hardly alone. According to a study of late-night talk shows released Wednesday by George Mason University’s Center for Media and Public Affairs, jokes about Romney are outnumbering jokes about Obama by a margin of more than 2 to 1.

What’s more, during the period from Aug. 27 to Oct. 3, 2012, when researchers also catalogued the political punch lines of Jay Leno, Jimmy Fallon, and Craig Ferguson—428 jokes in all—Letterman was by far the biggest Romney mocker compared with his relatively gentle treatment of Obama.

“The disparity was greatest on The Late Show with David Letterman,” the study reports. “Letterman told 44 jokes about Romney and 9 about Obama, a five to one margin.” The study adds: “Mitt Romney was the target of 148 jokes on late night talk show monologues, over twice as many as President Obama. Obama finished second with 62 jokes.”

The GOP standard-bearer “is leading in the humor race, but being the biggest joke is a race nobody wants to win,” says George Mason University Prof. Robert Lichter, who heads the Center for Media and Public Affairs and who has been tracking political jokes on television for more than two decades. “You could say Romney is the biggest, freshest face for comics to go after this year—and Obama’s been around for a long time,” Lichter says by way of trying to explain the disparity. “But even in 2008 [when a previous study was conducted], Obama finished behind Sarah Palin, John McCain, and George W. Bush. He came in fourth. Obama has always been treated kind of gently on these shows.”

As for why that would be true, Lichter ventures that the comedy biz is dominated by people whose political and cultural biases are more closely aligned with a so-called liberal Democrat. In other words, they might feel more connected to a cool, hip post-baby boomer who has admitted, in his youth, to smoking marijuana and doing “a little blow” than they do with a straight-laced Mormon in his mid-60s who won’t even sip a beer. “The conservatives who are funny tend to be libertarian types,” Lichter says. “Traditional conservatism is not a hotbed of humor. Honoring tradition and respect for authority does not lead to big yuks very often.”

Harry Shearer, star of This Is Spinal Tap and The Simpsons, endorses this theory. “Obama resonates with people who write for those shows—he’s attractive, smart, good at hoops—he’s them,” says Shearer, who hosts a weekly satirical public radio program and plays the title character in the British docu-sitcom Nixon’s The One. “Romney is a classic ‘suit’—and Mormon to boot. He’s so ‘the other.’”

Shearer has additional insights on the subject, but first here’s another Letterman joke: “They say that Paul Ryan will humanize Romney. And I thought, hell, an amoeba could humanize Romney.”

Let’s do another: “Mitt Romney is worth half a billion dollars and he’s saying he pays 13 percent annually in taxes. Al Capone paid more than 13 percent in taxes, ladies and gentlemen.”

OK, one more: “Lindsay Lohan has endorsed Mitt Romney. She is hoping for a presidential pardon.”

But back to Shearer, who guesses that there’s one other simple reason why Romney is receiving rougher treatment than his campaign rival: “I’m a fan of Occam’s razor. The easiest possible explanation is that Obama goes on their shows and Romney doesn’t.”

Indeed, Obama has done seven guest spots on Letterman, two of them as president. Romney, who mused in that notorious “47 percent video” that “Letterman hates me because I’ve been on Leno more than him,” hasn’t appeared on the Late Show since he was persuaded to read a self-immolating “Top Ten” list in March 2011. It was only his second visit. Letterman, for his part, has exhorted viewers not to vote for Romney until he returns as a guest.

“As with Washington insiders, access proves persuasive,” Shearer says. “Access and intimacy—or the illusion of intimacy—also breeds restraint. It’s almost a topsy-turvy universe. Satirists, at least the way I learned it, are supposed to make fun of the people with the power more than the people who aspire to power…Obama certainly has done a bunch of crappy things worth making fun of, like trampling civil liberties with a 21st-century bulldozer.”

Shearer dismisses the notion that race, even more than Social Security and Medicare, is the third rail of American politics and political humor, and that Obama should get an easier time from joke-writers because of his status as the first black president. “People on television for years have made fun of Oprah and other black celebrities. And Obama is still the president of the United States, the guy with all the power. Memo to the people who are worried about being called racists: Obama is only half black. You could easily make fun of the white half.”

Time for another Letterman joke: “Hookers in Times Square, God bless ’em, are offering a Mitt Romney Special. For an extra $20 they’ll change positions.”

The big question, of course, is whether his position as the butt of more than twice as many jokes on late-night television disadvantages Romney, compared with Obama, as the day of reckoning draws nigh. Or is the result as silly as the jokes themselves?

“The short answer is fairly straightforward,” says Jody Baumgartner, a political science professor at East Carolina University who studies the impact of political humor. “When jokes are made—particularly about a political figure, or a party, or a process, or an institution—people’s perceptions or opinions of the target of the joke go down. So it does matter. It absolutely matters.”

Which is to say, it’s prudent to take seriously when David Letterman remarks: “I’m having trouble warming up to Mitt Romney. He looks like the guy in the restaurant that comes to your table to make sure everything’s all right.”