The “Rally to Restore Sanity” was supposed to be a joke, a liberal parody of the huge “Restoring Honour” march organised in August by Glenn Beck, the conservative Fox News commentator and patriarch of the Tea Party movement.
But for the thousands of progressives and moderates expected to descend on Washington on Saturday, three days before the midterm Congressional elections that are expected to hand the House of Representatives back to Republicans, the rally has a serious point.
It has fast become a magnet for those alarmed at the Tea Party juggernaut, an assertion of leftwing values not seen since President Barack Obama was inaugurated 18 months ago.
“We are going to make history, fellow ralliers,” one of the attendees, John Hoover, wrote on the rally's Facebook page. “We are going stop the madness!”
The event is the brainchild of Jon Stewart, the liberal comedian-meets-biting political commentator who fronts the satirical Daily Show, who has described the rally as “Woodstock, but with the nudity and drugs replaced by respectful disagreement”.
“We’re looking for the people who think shouting is annoying, counterproductive, and terrible for your throat; who feel that the loudest voices shouldn’t be the only ones that get heard,” Mr Stewart says on the rally website, “and who believe that the only time it’s appropriate to draw a Hitler mustache on someone is when that person is actually Hitler. Or Charlie Chaplin in certain roles,” he added, referring to the Tea Party practice of adding facial hair to Mr Obama's photo.
His fellow comedian Stephen Colbert is holding an “opposing” rally at the same time, called the “The March to Keep Fear Alive” – but essentially the events are one.
The march will certainly have a comedic feel. There is a competition to come up with the funniest placard, with contenders including “Obama is a muslin” showing a picture of a white cloth – a play on the Tea Party accusation that president follows Islam – and “God Hates Hommos (it's too garlicky)”.
The Huffington Post, a liberal news website, is providing “sanity buses” from New York, and satellite rallies are being held as far afield as Chicago, San Francisco and Seattle.
A slew of American news organisations have even banned their journalists from attending in a personal capacity, something they probably did not have to do with Mr Beck's rally, perhaps underlining the Tea Party's point about liberal bias in the media.
The rally received the kind of advertising that money cannot buy this week, when Mr Obama appeared on the Daily Show. The interview, however, merely served to underscore how sensitive the president remains about liberal criticism that his administration's reforms have been too “timid”.
Indeed, while both men have pilloried the Tea Party movement and associated organisations – Mr Stewart has taken great delight in going after Fox News in particular – that is not to say that they have gone easy on the president.
But some commentators say the rally will only serve to enrage conservatives.
“There's still a lot we don't fully understand about the Tea Partiers and the political independents who have lost faith in Obama,” according to Timothy Noah, a commentator for the Slate website. “But one thing we should all be pretty clear on by now is that they hate, hate, hate anything that smacks of elitism. The spectacle of affluent 18-to-34-year-olds blanketing the Mall to snicker at jokes about wingnut ignoramuses and Bible thumpers will, I fear, have the effect of a red cape waved before a bull.”