Members of the “Draft Bernie” movement gather on Friday, before walking petitions to his office. (David Weigel/The Washington Post)

On Friday, as Sen. Bernie Sanders (I-Vt.) celebrated his 76th birthday, a crowd of about 60 people gathered on the Mall. They were part of the People’s Convergence Conference, which centered on the specific political goal of drafting Sanders to lead a “People’s Party” — a new, independent force — into the 2018 and 2020 elections. Nick Brana, the former Sanders political aide who had given up on Democrats after trying to wrangle superdelegates in the 2016 primary, smiled and thanked supporters who were about to help him deliver “50,000 plus” signatures to Sanders’s Senate office.

“Two years ago, this was unthinkable,” Brana said into a megaphone. “The establishment media attacks us all the time. Three days after we launched, MSNBC was on our case! They had a whole panel discussion about how Bernie shouldn’t do it.”

Very few members of the media were on hand as the Convergence kicked off. Brana’s campaign, which Sanders has repeatedly (albeit politely) rebuffed, is the best-organized of several efforts to turn progressives away from the Democratic Party. It has the endorsement of Cornel West, perhaps the 2016 Sanders surrogate most adamant about leaving the party; and it has two clear narratives, which suggest that to stay inside the nation’s major liberal party is to accept permanent decline.

One narrative, backed up by polling, is that voters feel no particular allegiance to the Democrats. “You’ve got the most popular politician in America, Bernie Sanders, encouraging people to join the Democratic Party; you’ve got Donald Trump, the most offensive politician in the country, also encouraging people to join the Democratic Party,” Brana said Saturday, at the Convergence’s main meeting on the American University campus. “And yet, the Democratic Party is declining; it’s declined in party affiliation since November.”

According to Gallup, which tracks party identification, this is true. The week of the 2016 election, 31 percent of voters identified as Democrats; as of last month, the number was down to 28 percent. Democrats, while improving their vote share in special elections all year, have continued to struggle with swing voters who consider elements of the party to be toxic.

Brana and Draft Bernie use that fact to gird a second narrative — that in the space of one or two elections, the Democrats can be replaced. Like many advocates of third parties, Brana has compared the current political climate to the 1850s, when a divided and discredited Whig Party imploded, and its exiles joined members of abolitionist parties to form the Republicans. A Draft Bernie promo video makes the analogy even cleaner, portraying Abraham Lincoln as a “progressive” representing a majority position. (Lincoln won 39.6 percent of the popular vote.)

With no support from Sanders — the senator has focused, with some success, on rallying Democrats behind single-payer health care — Draft Bernie used the weekend to put activists on display. After the rally on the Mall, dozens of activists marched to Sanders’s office to deliver the draft petition. “I’m expecting my old colleagues to welcome me with open arms,” Brana joked as the march began.

The march ended like most rallies at Capitol Hill offices. After trudging through metal detectors, activists met with Senate staff members who would let activists come in and speak, but were unable to engage in anything related to electoral politics.

“If you don’t think we need a third party, you’re not paying attention,” said the Young Turks video network host Jimmy Dore, revving up the crowd, which began singing “Happy Birthday” to Sanders.

The rest of the Convergence conference focused on long-term strategy, with notes of despair about how Sanders seemed content inside the Democratic caucus.

“The last thing we want to see is our dear brother Bernie Sanders becoming too comfortable and adjusted to the corporate wing, the Schumers, and the Pelosis, and the others,” West said at Saturday’s main panel discussion. “And the Hillary Clintons — I just took a look at her book. Everybody’s responsible but her!”

In interviews, several participants in the march said they were following Sanders’s work on single-payer health care; some viewed the draft campaign as an outside strategy, complementing Sanders’s inside strategy, and keeping Democrats honest and scared.

Brana was more pessimistic. At Saturday’s panel discussion, he cited the inability of California Democrats to pass a single-payer bill — an issue that has riven the party in California, with the Sanders-backing California Nurses Association launching waves of protests — as a preview of any future where Democrats are allowed to take back power.

“Medicare for all has been in the California Democratic platform for decades,” Brana said. “Yet somehow, they manage to never actually pass it!”

All of the evidence, he added, pointed to a split from the Democrats, modeled on Sanders’s own success in Vermont. “Here’s a guy who spent his whole life proving that independents and third-party candidates can make a difference; now, we just want to remind him of it,” he said.