"It was always going to be Joe Biden," said U.S. campaign professional Joe Trippi, who has advised Democrats for decades.

Trippi stayed out of the primary campaign this season, but he's seen enough of them to know that there's always a gut-check moment when he says Democrats ask themselves this hard question before committing their vote: "Holy crap, are we really gonna do that?"

Former vice-president Biden is the presumptive 2020 nominee because he passed the gut check. His rival, Sen. Bernie Sanders, isn't because he didn't. At least, that's part of the story.

If you've been following the Democratic presidential primary and yet were surprised when it tidily wrapped up with Sanders's exit this week, that might be because the punditocracy generally misled you, once again, about the strength of the Sanders campaign.

Pundits overcorrected

The first time Sanders ran for president, in 2016, pundits wrote him off as too far left, before anyone had cast a single primary vote. But Sanders turned out to be a formidable challenger to front-runner Hillary Clinton.

The pundits got it wrong again this year when they overcorrected and very nearly handed Sanders the nomination while there was still snow on the ground in New Hampshire, apparently believing the party was moving inexorably in Sanders's direction.

Sanders and former U.S. vice-president Joe Biden greet each other at the Democratic presidential primary debate on March 15. (Evan Vucci/The Associated Press)

The "garbage in, garbage out" rule means any analysis built on those two mistaken assumptions is probably wrong, too. So there is some rethinking going on about why Sanders was underestimated in 2016 and overestimated in 2020; what really happened and what it means for the party in the general election in November.

As they did in 2016, some Sanders supporters claim that their man was railroaded out of the nomination by a party establishment disdainful of his grassroots movement.

After Sanders dropped out Wednesday, for instance, his national press secretary, Briahna Joy Gray, suggested Biden had been installed as the nominee by the Democratic Party leadership. She also retweeted a Fox News clip that asked whether Biden could "find his car in a three-tiered parking garage" or "navigate a salad bar," let alone lead the country.

Bernie was too kind to go after Biden, but it's coming.<br><br>Either Dem leadership cares more abt maintaining a corporate status quo than getting rid of Trump, or they're planning to replace Joe - adopting a pretty fast and loose relationship w/ representative Democracy. <br><br>Lose lose. <a href="https://t.co/mzQYMjM2Nc">https://t.co/mzQYMjM2Nc</a> —@briebriejoy

But if you cross-check the 2020 primary results with the 2016 results, it's clear why Sanders isn't the nominee: in every primary election — every single one — Sanders did worse this time than he did last time, sometimes a lot worse.

Doubts about enacting Sanders's policies

"Parts of the electorate who were supporting him in 2016 were not necessarily supporting Bernie Sanders's ideas, they just didn't want Hilary Clinton to be the nominee," said John Hudak of the Brookings Institution, who last month compiled the stats for a paper on Sanders's two primary campaigns.

Without the anybody-but-Hillary advantage, Sanders faced closer scrutiny this time. His progressive proposals — Medicare for all, free college education and the like — weren't necessarily unpopular. Lots of voters liked the things he wanted to get done, but they weren't convinced he knew how to get them done, Hudak said.

"Bernie Sanders has never in his career thought about process. That's why he's been a wildly unsuccessful legislator for 30 years."

The Sanders campaign has said it's misleading to compare results from 2020 to results from 2016. The field was much wider this year and so naturally more fragmented, they say. But the fact is, some primary voters supported Sanders because they didn't have any other not-Hillary option in 2016. And when they did have other options in 2020, they chose someone else.

Couldn't secure African-American vote

Sanders seems not to have understood the nature of his success in 2016, Hudak said. "That led to a series of strategic errors that ultimately left him as a runner-up again in 2020."

The main strategic error, Hudak said, was not realizing that Clinton ultimately beat him in 2016 because she swept the African-American vote, especially in southern states. Sanders had five years to fix that problem, but didn't, and it cost him dearly.

WATCH | Bernie Sanders announces the end of his 2020 campaign

Bernie Sanders announced the end of his campaign to be the Democrats’ candidate for president after being unable to gain momentum during the COVID-10 pandemic. 1:59

Trippi said it might have been different had Sanders competed against any candidate, other than Biden, for African-American votes.

"Everybody else gave Sanders a fair fight with African-Americans, but against Joe Biden, good luck, buddy," Trippi said.

"Just like Joe Biden wasn't going to win the fight for young progressives against Bernie Sanders, right? That's not going to happen."

Potential lessons for Trump

When Biden won South Carolina in a landslide thanks to African-Americans, some progressives behaved as though black voters didn't understand their own self-interest. This prompted a scorching, sarcastic public backlash from Michael Harriot, a columnist with the black politics and culture site The Root, aimed right at Sanders supporters. It seemed to confirm they had little in common.

"And now your fragile brittle hearts are broken into a thousand little pieces because black people have rejected the Buddha of Birkenstock-wearers during his quest for the presidency. And by not choosing Bernie Sanders, Joe Biden supporters are somehow ruining America," Harriot seethed in his open letter to so-called Bernie Bros.

This reconsideration of Sanders' success in 2016 — as partly a by-product of the anybody-but-Hillary feeling, and the gender bias that includes — could be bad news for Donald Trump as well, because, obviously, Biden is not Clinton.

U.S. President Donald Trump owes much of his victory in 2016 to many voters' antipathy to Hillary Clinton. (Jonathan Ernst/Reuters)

Consider Michigan. Clinton lost the state narrowly to Sanders in the 2016 primary and then lost it even more narrowly to Trump later in the general election.

But Michigan apparently likes Biden a lot. He beat Sanders handily there this year. That's a flashing red warning light for Trump, because Michigan remains an important step on his path to a second term.

The Clinton factor

So the story of Sanders now seems, to a greater extent than before, a story about Hillary Clinton. Without Clinton to run against, Sanders wasn't as competitive this year, and without her to run against, Trump might not be, either.

"It was Hillary Clinton at the top of the ticket [in 2016]. Which is sort of sexism on steroids — it's not only that it's a woman, but it's that woman," said Hudak.

Analysts say Sanders was hobbled in the 2020 race because he wasn't up against Hillary Clinton. (Alex Brandon/Associated Press)

"And that was a boost for [Trump in 2016], whether it was in his support or a fall-off in Democratic support, and this year he's not going to have either."

Sanders supporters are again wounded, disappointed and in some cases angry. But they have time to recover between now and election day, and some already seem to be looking to the battle against Trump in November, and other battles beyond.

After Sanders ended his campaign on Wednesday, Jonathan Tasini, a former Sanders surrogate, tweeted, "For all those whose cares have been our concern, the work goes on, the cause endures, the hope still lives and the dream shall never die."

I recall what Ted Kennedy said in 1980 after losing to Carter: "For all those whose cares have been our concern, the work goes on, the cause endures, the hope still lives, and the dream shall never die" <a href="https://twitter.com/hashtag/ThankYouBernie?src=hash&ref_src=twsrc%5Etfw">#ThankYouBernie</a> <a href="https://twitter.com/hashtag/StillSanders?src=hash&ref_src=twsrc%5Etfw">#StillSanders</a> <a href="https://twitter.com/BernieSanders?ref_src=twsrc%5Etfw">@BernieSanders</a> —@jonathantasini

And should anyone be unfamiliar with those lines, Tasini pointed out they were spoken by Ted Kennedy — a progressive and the embodiment of the Democratic establishment — at the 1980 Democratic convention.