"Candidates have figured out that you can reach voters through entertainment venues even better than news," said Robert Lichter, a George Mason University professor and head of the Center for Media and Public Affairs.
Candidates made 110 appearances on the late-night shows, up from 25 in 2004, the center said. Fifty this time came before a primary vote was even cast, as a full complement of candidates in both parties looked for ways to get their faces in front of cameras - something President Bush didn't have to worry about four years ago.
There's a rich history of candidates using entertainment venues to show voters they can laugh at themselves: Richard Nixon went on "Rowan & Martin's Laugh-in" in 1968, and Bill Clinton played the sax on "The Arsenio Hall Show" in 1992. Yet it wasn't until 2008 that the appearances began to seem routine.
Republican John McCain made 17 such guest shots on venues that relentlessly made him the butt of jokes, although one appearance he canceled - with Letterman - may be remembered longer than any of them. President-elect Barack Obama had 15 appearances, third behind Republican Mike Huckabee, who now has a talk show of his own on Fox News Channel.
For the shows, it was a way to tap into a campaign that was a television hit from start to finish. Leno had 22 candidate appearances, while Stewart had 21, Letterman had 19 and Stephen Colbert had 15.
Not only does a candidate have the chance to display a sense of humor to the late-night crowd, a good exchange could be magnified with endless repeats on YouTube or cable news networks the next day.
The shows also give the candidates a venue to talk directly to voters than they might otherwise get. In 2000, candidate George Bush had more time to talk in one appearance with Letterman than he had during a full month on the "CBS Evening News," Lichter said. And who wants to deal with pesky journalists, who always want to knock you off message?
"It's a lot more risky, as Sarah Palin will attest, to do an interview with Katie Couric than it is with Jay Leno," said Howard Wolfson, a veteran campaign strategist and former Hillary Clinton adviser.
They aren't always puffball appearances, though. Letterman, in particular, has become a particularly sharp interviewer. When McCain backed off an appearance citing the economic crisis - then did an interview with Couric later that day - Letterman wouldn't let him forget it until McCain came back and pleaded for forgiveness. At a crucial time, Letterman was repeatedly reminding viewers of McCain's brief campaign suspension, a period the candidate would rather voters have forgotten, Lichter said.
His running mate stayed away from the talk shows but made one memorable appearance on "Saturday Night Live," getting in on some jokes about her.