The dynamic duo of Comedy Central seem to have a similar Woodstocky vibe in mind — with fun and music — but they are also entering uncharted territory by seeming to elevate ironic detachment to the level of a political manifesto. One danger is that a rally that doesn’t meet the sky-high expectations of 200,000 attendees could undercut the hard-won reputations of both Stewart and Colbert for using comedy to speak truth to power in a way that traditional journalism has failed to do over the last decade. But a bigger issue is treating the challenges of 2010 — from rising poverty to unending war in Afghanistan to global warming, which are every bit as serious as those confronted on the National Mall in 1894 or 1963 or 1969 — with little more than humor and intellectual distance.

When King and his fellow marchers returned home from the Mall to the Deep South 47 years ago, they knew they faced nightsticks or worse on the rocky road toward the Voting Rights Act of 1965. Today, the challenge facing rallygoers is, as Stewart suggests, asking “the sitter if she can stay a few extra hours, just this once.”

Ultimately, it will be those kids at home who learn the history of whether 2010 was just an autumn of harmless entertainment or the throes of a nation amusing itself to death.