Are Jon Stewart and Stephen Colbert going all serious on us?

The Comedy Central's Jon Stewart and Stephen Colbert are drawing closer to the institutions they love to mock. President Obama even gave a nod to their upcoming rallies in Washington. When that happens, they need to retreat, analysts advise.

As the embrace deepens between comedy and politics this election cycle, Comedy Central’s satiric duo, Jon Stewart and Stephen Colbert, are inching ever closer to the very institutions they delight in mocking.

Jon Stewart actually landed a nod from President Obama, who last week name-dropped his upcoming only-half-mock “Rally to Restore Sanity” – with a few garbles – during a chat with college students. He's also practically a political éminence grise, with New York magazine putting him on a September cover and proclaiming this to be the Jon Stewart decade.

Then, not to be missed was political commentator Ariana Huffington’s nod of support for Stephen Colbert last week, on the heels of the comedian’s jaunt up to Capitol Hill to testify at a congressional hearing on migrant workers' rights.

All of this sober straight-talk about two TV pranksters raises this ticklish question: Are the jesters circling a tad too close to that tricky line between funny and serious? After all, it is possible to cross that divide, as jokester Al Franken showed when he jumped from "Saturday Night Live" funny man to senator from Minnesota (reportedly, he often makes the extra effort not to tell jokes so that his colleagues will take him seriously).

“It is a genuine worry,” says Amber Day, author of “Satire and Dissent: Interventions in Contemporary Political Debate.” Crossing over into Serious Land could cost the satirists part of their audience, which likes them precisely because they expose the degree to which politicians can be stage-managed and inauthentic. “If they start to become part of that establishment," she says, then their humor "loses its power.”

They are running a bit of a risk with their dueling political rallies, which are being trumpeted by liberals, in Washington on Halloween weekend. The events are still four weeks away, but one-third of the public has heard something about them, according to a recent survey by the Pew Research Center for the People & the Press.

At the moment, Ms. Day says, Stewart and Colbert are managing to avoid the danger zone of seriousness. “I think they are going to try very hard [not to walk up to that line].... They will continue reminding everyone they are comedians making silly fart jokes and trying not to be entirely respectable, partially because that’s what they do but also in a semicalculating way they have to,” she says.

The satirists are at their least effective when they are doing live coverage, as would be the case at the upcoming rallies, says Geoffrey Baym, author of "From Cronkite to Colbert: The Evolution of Broadcast News." "They derive their credibility from their outsider status,” he says. “They are the kid throwing spitballs.” Losing the outsider stance by becoming so engaged with a message and a serious tone would actually undermine their power to persuade, he says.

When politicians start to endorse the comedians' ideas, the only position for Stewart and Colbert to take is to retreat, says branding expert Adam Hanft, creator of the political website www.spinseason.com. Stewart "will have to distance himself from any appearance of being too cozy" with the political establishment, he says.

That's just what Stewart did on his show Thursday night, after Obama mentioned his rally. First, he crowed at the reference. “Yesssss,” he laughed. “President Obama just plugged the rally.”

But then he poked fun at the Democratic president’s jumbled title for the rally, saying he would probably have to use the commander-in-chief’s new rally name: “Rally for American in Favor of a Return to Sanity or Something Like That.”