Every year since 2000, Tyson Manker has voted for the winning presidential candidate. And this year, he’s got his sights set on Bernie Sanders.

Manker, a Marine Corps veteran, co-founded the group Veterans for Bernie and said he’s confident the Vermont senator will make it to the Oval Office.

“You could say I’ve got a pretty good history of picking the president, and my support is enthusiastically 100 percent behind Bernie Sanders,” he said. “I expect him to win the nomination.”

Manker isn’t alone. According to organizers, more than 150,000 people have RSVP’d for house parties Wednesday evening to listen to a simulcast from the Democratic presidential candidate and coordinate their volunteer efforts. And what Sanders lacks in funds—he raised about $15.2 million this quarter, while Hillary Clinton raked in more than three times that figure—he may make up in true believers with experience in grassroots organizing. This is not a fluke; some of the most dogged pro-Bernie volunteers are alums of the Occupy movement, where they honed their activism skills.

“The graduates of Occupy are now skilled organizers,” said Katherine Brezler, a Yonkers schoolteacher and national digital organizer at People for Bernie.

She said some of the core organizers at People For Bernie—a grassroots group unaffiliated with Sanders’s campaign that works to mobilize Sanders volunteers—first met in Zuccotti Park during the 2011 Occupy Wall Street protests.

“After Occupy, people didn’t just go and sit in a hole,” Brezler said. “After Occupy, people became very involved in their communities and broadened their skill sets, broadened their networks, and now are revisiting a new campaign with revived interest in electoral politics because the candidate is speaking the language of their issues.”

There are numerous constituency groups in the People For Bernie family, said organizer Stan Williams. They range from those representing essential constituencies—including Women for Bernie, African Americans for Bernie, and Labor for Bernie—to slightly more niche groups (the Deadheads for Bernie Facebook page had 1,308 likes at press time). And they relish their independence from the official campaign.

“You could write terrible things about me and no one’s going to care because I’m not Bernie,” said Charles Lenchner, one of the co-founders of People For Bernie. “We’re free. We use that freedom to do what we can.”

That includes curating social media content, training constituency groups, helping smaller organizations write press releases, and generally cheerleading pro-Bernie efforts around the country. They also reach out to some constituencies where Sanders has struggled—especially African-American voters. Nadya Stevens, who works with African Americans for Bernie, said her group is angling to increase Sanders’s name ID among black voters while reminding them of the damage that Bill Clinton’s tough-on-crime policies incurred.

“The Clinton administration—and that includes Hillary—did some terrible things that adversely impacted the black community,” she said.

She added that she thinks Bill Clinton recently apologized to the NAACP for that legislation because it was the politically expedient thing to do.

“I think that he’s doing that for Hillary because Hillary’s not going to do it herself,” she said.

As for organizers’ levels of confidence in the likelihood of a Sanders presidency? They vary.

“I have so little faith in the system to begin with,” Lenchner said. “I would just say that an election is an opportunity to organize, and the organizing that we’re doing is likely to have an impact for years to come.”

Brezler, the Yonkers schoolteacher who said she spends 19 hours a day working on the pro-Bernie efforts because school is out, is more bullish.

“I’m really excited about this possibility and I believe that we will win,” she said.

She added that volunteers are in for the long haul.

“We also know that it’s important to practice self-care and to encourage your teammates to go for a walk, and to check in and have a normal non-Bernie conversation from time to time with people,” she said.

“At the end of the day, Hillary supporters will be Bernie supporters after the primary,” she added.

But not all Sanders backers would jump to Team Clinton. Manker, an independent who voted for both Bush and Obama twice, said he would consider voting Republican again if Democrats nominate Clinton.

“I have yet to meet or speak with a single veteran or military person who supports Hillary Clinton for president,” he said, adding that Clinton’s false claims that she ran through sniper fire in Bosnia still anger veterans.

“That’s not a minor deal,” he continued. “That has not gone away. For everyone who has ever served in combat, to attempt to put herself in our shoes without ever taking the time to hear our stories does a disservice to all of those who have given their lives and have served in the line of duty.”

“Nothing bugs a combat veteran more than someone claiming to also be a combat survivor who wasn’t,” he added.

And Rand Wilson, a volunteer at Labor for Bernie, has found hope in a funny place.

“Who would think that Donald Trump would be taken seriously?” he said. “If you’d asked me two months ago, is anybody going to take Donald Trump seriously, I would have said, ‘Are you crazy?’ That guy’s out of his mind. But look what’s happening. It’s weird.”

Winnie Wong, a co-founder of People for Bernie, said the next two months are key to their efforts, and that the crowds and volunteers Sanders has attracted mean his presidential prospects are likely being underestimated by the political media.

“This is unprecedented, this is amazing,” she said. “And what happens next, I think, will be historical.”