WASHINGTON — Jon Stewart and Stephen Colbert, the founding fathers of fake news, drew throngs of exuberant supporters to Washington on Saturday for a joint rally that crowded streets, taxed the transit system and flooded the Mall.

With midterm elections looming and Democrats bracing for a historic thumping, the two comedians reined in their three-hour show to nonpartisan bits, musical entertainment and gentle ribbing of the purported enemies of incivility. The denizens of the Capitol, visible behind the stage, escaped their usual excoriation.

But at the rally’s conclusion, Stewart changed his tone and his outfit. Having swapped a black T-shirt and blazer for a suit and tie, the comedian argued that the rally’s target was the caustic level of discourse in Washington, and its nasty echoes on cable television’s 24-hour news cycle. Stewart said that noisy debate obscured a reality that he perceived: that everyone throughout the country had found a way to work together.

“The only place we don’t is here or on cable TV,” said Stewart, putting much of the blame on Washington. In earnest terms that bordered on political rhetoric, he orated, “If we amplify everything, we hear nothing.”

Stewart and Colbert built their stage on the opposite end of the Mall from the Lincoln Memorial steps, where conservative commentator Glenn Beck led a similarly vast and homogenous crowd two months ago. That rally, with its religious theme of “Restoring Honor,” had conservative political undertones and prompted Saturday’s satiric response.

The two rallies represented two distinct television audiences and self-identifying political constituencies.

“This is my comedy channel,” read a sign emblazoned with the Fox News logo, hoisted by Steven Crawford, of York, Pa. The other side of the sign, illustrated with a Comedy Central logo, read: “This is my news channel.”

Democratic and Republican leaders argued that the comedic rally either boosted reserves of Democratic enthusiasm, or exhausted it by drawing potential door-knockers away from battleground states, all for some laughs on the Mall.

Rep. Chris Van Hollen, D-Md., who is tasked with preserving the House Democratic majority, expressed optimism that the rally “boosts energy among younger voters,” adding that “anything that boosts participation among young voters is a good thing generally, and given how they largely voted in 2008, good for Democrats.”

Young voters have increasingly turned to Comedy Central’s “Daily Show” and “Colbert Report” for political news, but in the days before the rally, observers of the political-media complex sought the larger goal of this unusual gathering: Would visiting progressives of all ages actually take political marching orders from comedians?

The question turned out to be moot. In their closing remarks, neither Colbert nor Stewart was explicit in his demands. “Your presence is what I wanted,” Stewart stated simply.

Showing up wasn’t simple, in a weekend that was packed with activities related to Howard University’s homecoming, the Marine Corps Marathon and Halloween. Many rally-goers encountered severe transportation delays.

Those who did get to the Mall found large portions closed off by metal fencing, leading to frustration at many usual entry points. Along one stretch, between Third and Fourth streets northwest, dozens of people scaled fences and portable toilets to get a better stage view.

Authorities would not estimate the crowd size, though the National Park Service decided to open an extra section of the Mall that was not included on the initial 60,000-person rally permit, according to Bill Line, spokesman for the Park Service. By 2 p.m., Metro ridership had already reached 330,000 people, comparable to an entire day’s tally for a usual Saturday, according to Metro spokeswoman Angela Gates.

As for the diversity of the crowd — the lack of which was the source of much criticism of Beck’s event — Stewart joked that it was absurd to read any motives of racism in a crowd’s demographics. But despite “Daily Show” correspondents dispatched in the crowd to cheekily interview an ethnically diverse sample of rally-goers, the crowd appeared overwhelmingly white.

“It’s very white,” said Tahir Messam, a 25-year-old computer expert from Brooklyn, who is African-American and came with Pakistani and Chinese friends. “But most of America is white.”