Bernie Sanders is the most popular senator in America, according to the last 11 Morning Consult polls, a distinction that may say as much about the institution and its fall from grace as the curmudgeonly junior senator from Vermont.

The Brooklyn-born Sanders is a man of many myths, chief among them that his fans believe the Democratic nomination was stolen from him in 2016, and that he’s still an outsider despite being in Congress for 30 years.

Until Joe Biden entered the presidential race, Sanders was the frontrunner. He had the highest poll rating and he’d raised more money than any of the other candidates. The latest Morning Consult poll has Sanders at 20 percent among Democratic primary voters, 18 points behind Biden. It’s early of course, but the ranking foreshadows another epic battle between an avatar of the establishment and a campaign driven by grievance—supported this time by many fans who believe that the 2016 nomination was rightfully his, and that he could have saved the country from Donald Trump if it weren’t for an out-of-touch and corrupt Democratic establishment.

Sanders is discovering that not all his 2016 support is transferable to 2020, says Dave Wasserman with the non-partisan Cook Political Report. Four years after his stunning rise in the polls, this year’s effort lacks that novelty. Democrats influential in the national party are wary of nominating someone whom President Trump can so easily caricature as the candidate of Venezuela. Sanders is in his late seventies now, which adds to doubts that he can deliver as a change agent.

“And he’s not a Democrat,” says Wasserman. “He’s leading an insurgency against the Democratic Party.” The longtime Democratic Socialist, who has caucused with the Democrats without joining them, did sign a statement in March asserting he is a member of the party now and would serve as one if elected president. But one part of his appeal has been the idea that the Democratic Party has been co-opted by corporate interests and has rigged the game against him.

“I think his message was the right message, but he was the wrong messenger," said a former Sanders aide, now speaking in the private sector. “It was a little bit of a protest vote” in 2016, the aide added.

“He brought about an enormous change in the Democratic Party or at least was a catalyst for it. He moved the Overton Window—he shifted the terms of debate. Before 2016 his ideas were dismissed as crazy leftist talk—he had the courage to say, ‘I’m a democratic socialist,’ and he forced people to talk about it.”

The looming problem for the party in 2020, says Wasserman, is that the Berniecrats aren’t going to stand down if the Democrats turn him down again.

“They’re going to have the same level of disgruntlement that cost Hillary the presidency,” he says, adding, “It is a serious problem for the Democratic Party.”

Sanders was no longer a viable challenger by March or April of 2016, meaning he could not mathematically catch Clinton in delegates. But he stayed in the race, raising money and taking shots at Clinton. And who can forget the angry “Bernie or bust” presence at the Democratic Convention in Philadelphia, raining on Hillary’s parade?

The 2016 Cooperative Congressional Election Survey found that fewer than 80 percent of Bernie voters cast their ballot for Clinton, and 12 percent of them voted for Trump. Trump’s margin of victory in the three states (Pennsylvania, Michigan and Wisconsin) that gave him his electoral victory was smaller than the number of Bernie voters who opted for Trump. Shocking, yes; unusual, maybe not. A 2010 Public Opinion Quarterly survey found that 25 percent of Hillary Clinton’s voters in the 2008 Democratic primaries voted for Republican John McCain in the general election, and not Barack Obama.

They were convinced that a Clinton-centric Democratic Party had cheated their candidate out of the nomination. And, to a degree, they had a point. Sanders had legitimate grievances with a party he wasn’t a member of treating him like a party-crasher. The DNC rigged its debates for maximum under-exposure to protect its cosseted frontrunner, which Sanders turned to his advantage, stoking voter resentment against Clinton as the establishment.

Even so, Sanders lost fair and square. And if you harbor doubts, Jim Kessler, a co-founder of Third Way, a moderate Democratic group, can share his spreadsheet on the 2016 primary vote. Clinton finally won 16.4 million votes to Sanders’ 12.7 million votes.

Sanders did better than he should have in 2016 in the caucuses, where the Clinton campaign was asleep and where activists have the upper hand. After party reforms, there will be just seven caucuses in 2020, compared to 17 last time.

Sanders lost the popular vote in primaries 57 to 43 percent. “The truth is that Bernie Sanders lost so badly in the primaries because he did horribly with African-American voters, that’s what did him in,” says Kessler. “She won by several million votes among African-Americans.”

The claim that Sanders was not treated fairly should be examined as well, Kessler adds. “Clinton treated him so gingerly, she never went after him. She thought she had the nomination sewed up. There were no negative ads against him, no serious opposition research that the Clinton campaign deployed. The media kept hands off on him. It’s different this time—they’re looking at his ideas like they’re serious, and they don’t hold up.”

Videos showing Sanders’ affinity for the repressive Sandinista regime in Nicaragua in the 1980s recently surfaced again. One clip has Sanders praising bread lines as “a good thing. In other countries people don’t line up for food: the rich get the food and the poor starve to death.”

Sanders’ record in Congress over three decades is also getting renewed attention. He first won Vermont’s at-large House seat in 1990 by making a deal with the NRA to oppose a waiting period for handgun sales, gaining him the gun rights group’s endorsement and defeating Republican Peter Smith who held the seat, and who had decided to support a ban on assault weapons. Sanders voted against the Brady bill in 1993 and for legislation granting gun manufacturers immunity from lawsuits in 1995.

As chair and then ranking member on the Veterans Affairs committee, Sanders has been a bulldog in getting veterans more choice of care, and pushing through major reform of the VA system, but only three pieces of legislation that he sponsored as a senator became law: a cost-of-living adjustment in 2013 to increase veterans’ compensation, and two bills to name post offices including one in Danville, Vermont, named after Thaddeus Stevens, an anti-slavery Republican who was born in Vermont and who secured the articles of impeachment against President Andrew Johnson.

Trump wasn’t in the White House when Sanders first ran, which is one reason that the scrutiny is tougher this time. The media was all over Sanders for saying prisoners should be allowed to vote, even the Boston Marathon bomber.

In 2016, Sanders endorsed Clinton, but it was mid-July, late enough in the process to give Trump a head start. He coupled his endorsement with an appeal to his supporters to continue the revolution he had begun. This time, the revolution may not be his to continue.

“None of us can afford to be Naders this time,” says Paul Equale, a former lobbyist and longtime Democrat, recalling the 2000 election when Ralph Nader running on the Green Party line took enough votes away from Al Gore in Florida to swing the election.

“I don’t blame Bernie Sanders for Hillary’s loss but this time he has a chance to be Ralph Nader, to really screw it up—and it’s not a role anyone who is aware of history should want to play. If he doesn’t win the nomination, and I don’t think he will, he better not be a spoiler.”