PHILADELPHIA — It was a cattle call that only a few presidential candidates answered. And while the front-runner was away in New Hampshire campaigning, the conference probably wouldn’t have welcomed former Vice President Joe Biden anyway.

Just four Democratic hopefuls traveled to the City of Brotherly Love to address the progressive faithful Saturday at Netroots Nation. Sen. Kirsten Gillibrand of New York, former Housing and Urban Development Secretary Julian Castro, and Washington Gov. Jay Inslee made the trip. All rank at less than 1% support in the polls. The only top-tier candidate to attend: Sen. Elizabeth Warren.

Rachel Earnest is with her. Like others who attended, the Pennsylvania voter told RealClearPolitics she can’t stand the thought of “another white guy in the White House.”

And while Biden launched his campaign in this city two months ago, promising to reject anger and embrace unity, this progressive congregation is united by a righteous, if occasionally vulgar, indignation. Lest anyone misunderstand, during a breakout session Michigan Democratic Rep. Rashida Tlaib reiterated her swearing-in night promise regarding President Trump: “We’re going to impeach the MF’er, don’t worry!”

This is a small sampling of the rhetoric from the premiere political convention for progressives. But at a moment when the Democratic Party has shifted farther left than ever before, what are we to make of the fact that less than a quarter of the candidates eager for a chance to challenge Trump bothered to show up? Is it due to the difficulty of marrying progressive policies with the populist energy needed to win back the White House? Sen. Sherrod Brown, who represents Ohio and who flirted briefly with a run of his own, disagreed.

“It isn’t a choice between a progressive message and talking to workers,” he said. “It’s about wages. It’s about overtime. It’s about work schedules. It’s about retirement. Our candidates talk about those things, and we win white workers, black workers, Latino workers, and Asian workers.”

Brown told RCP that “you can get a majority damn near everywhere in the country if you respect and honor work, and talk to workers that way.”

All the same, he wishes more of the candidates would have joined him on stage. Though he understands demanding campaign schedules, skipping out on Netroots “is a missed opportunity for people not here.”

Trump is progressive enemy No. 1 in the halls of the Philadelphia Convention Center this weekend. And the Democratic brass is a close runner-up. The activists and community organizers and voters in attendance seem hell-bent on knocking out both come 2020.

Halfway through a session hosted by the Democratic National Committee about mobilizing the grassroots for the general election, about two dozen protesters jump to their feet and start chanting. “We demand,” the leader shouted. “We demand,” the others echoed, “a climate debate.” After about a five-minute interruption, DNC National Training Director Cheyenne Davis interrupted those interrupting her to meekly say she welcomed the one-sided discussion.

Angered that climate change only received limited billing at the first sanctioned Democratic primary debate, those who crashed Saturday’s event said they feel used.

“They see us as people who can be appeased with some statement about climate change -- that it is real and that we should return to the Paris Agreement,” RL Miller, co-founder of Climate Hawk Votes, told RCP. Addressing the issue will require more, specifically a debate about specifics, be it a carbon tax or a Green New Deal or the future of modern agriculture.

Though having an open discussion about their preferred policy might mean alienating moderates and even losing the election, it’s a gamble the protesters downplay are willing to take.

“The DNC is afraid of losing Obama-Trump voters,” said Miller, referring to voters who switched party allegiance between the 2012 and 2016 presidential elections. “They are afraid that if the Dems all get on stage and try to out-progressive each other, they are going to hear ‘carbon tax’ and lose all those Obama-Trump voters in Ohio. We are going to start talking about banning fracking, and we are going to lose all those Obama-Trump voters in Pennsylvania. We talk about abolishing [internal combustion engine] cars, and there goes Michigan.”

Inslee seems convinced, instead, that climate change is a weak spot in the armor of the Trump campaign. And though he polls at less than 1%, the Washington governor told reporters he will keep pushing for a separate debate to address increasing global temperatures. He will keep the pressure up but he won’t “burn his DNC membership card” just yet.

Many of the protesters support him and are members of the Sunrise Movement. Most are also young. Their parents were too afraid of coming across as too liberal, explained Mattias Lehman, digital director of the group that gained infamy in Democratic circles for occupying the office of House Speaker Nancy Pelosi earlier this year.

“Look, nobody’s going to just give our generation political power. We ain’t waiting for the torch to pass,” Lehman told RCP. “We are building a youth movement. They don’t come to us, we come for them.”

Party loyalty doesn’t count for much at Netroots, where progressives consider insurgency more honorable than serving as a loyal foot soldier in the campaign to drum Trump out of the Oval Office. Philadelphia City Councilwoman Helen Gym made that clear from the main stage ahead of the presidential forum.

An unnamed power broker told her that she and the far left represented “the biggest threat to the Democratic Party” and she didn’t disagree: “I told him, ‘Damn right.’” The crowd erupted.

A longtime party loyalist, Gillibrand travelled to Philadelphia to offer penance to the progressive congregation for her own white privilege.

"Now as a white woman, who has certainly experienced enormous amounts of white privilege, I travel with a staff member who is black, and I see how she is being treated differently when we walk into a hotel. I see it, and it infuriates me," Gillibrand said, raising her voice.

The New York senator also talked about her own son, who will have “moments in his life that his whiteness protects him. His whiteness changes how he's treated. When he walks down a street in a hoodie with a bag of M&Ms in his pocket, he won't be shot."

The liberal crowd was supportive and offered appreciative, yet moderate, applause. They had no such restraint for Warren.

The Massachusetts liberal was the undisputed favorite at Netroots, and the conference was clearly her home turf. So much so that when protesters interrupted her, complaining about the treatment of illegal immigrants under the Obama administration, the crowd self-policed, shouting, “Let her finish.”

“This is our moment to live our values and that means down at the border when people come here who are desperate,” Warren said, “then we need to treat them with humanity, and we need to follow the law.”

The progressive lawmaker added that mistreatment of border crossers might be tolerated now because “Donald Trump may be willing to look the other way,” but “President Elizabeth Warren will not.”

The crowd erupted.