After 2016, the Democratic establishment would have been justified in getting out of the business of presidential politics.

It swung so strongly behind Hillary Clinton that it discouraged any serious contenders from getting in the race. Her competition was a motley collection of people who didn’t get the message or didn’t care — including a no-hope socialist from Vermont named Bernie Sanders.

Because politics abhors a vacuum, Sanders became the anti-Hillary candidate and the leader of a movement that four years later threatens to take over the Democratic Party.

But that’s getting ahead of the story. Fortified by endorsements from anyone who mattered and the lockstep support of Democratic donors, with even the debate schedule fashioned to suit her ­interests, Hillary won the nomination as scripted — and proceeded to lose the general election to a ­rival who had a 37 percent approval rating on Election Day.

Having thrown in with an underperforming candidate in 2016 who had been a fixture in national politics for decades and never shown much ability to inspire voters, the Democratic establishment turned in 2020 to … Joe Biden.

No one was clearing the field this time around; in fact, the ­opposite. So if the former vice president is as forlorn as he currently seems, he will be an asterisk in a field that moved on without him, rather being propped up as the nominee despite his manifest weaknesses.

Perhaps Biden will perk up once the race gets to more demographically favorable terrain in Nevada and South Carolina, but at this juncture, he looks like a parody of an overhyped establishment front-runner.

Biden’s campaign couldn’t have been more conventional. It was built on his résumé, particularly his eight years as Barack Obama’s veep. It centered on electability and his polling versus President Trump, both important, but neither prone to inspiring people.

It was tightly controlled, limiting access to the candidate on the premise that he couldn’t be trusted to be more freewheeling and could win the nomination going through the motions. Finally, it hewed to ­existing Democratic orthodoxy.

This model of a campaign is ­always vulnerable to upstart challengers who find new ways to ­activate and move voters and think beyond cookie-cutter tactics and content.

Throw on top Biden’s obvious failings as a political performer, and it’s no wonder that he has been eclipsed by a Bernie Sanders who commands fervent support and a Pete Buttigieg whose message of uplift and generational change has found an audience.

The greatest strength of the Biden campaign was always its national polling. But national polling doesn’t determine who wins the early states, whereas the results in the early states affect the national polling. Sure enough, after his dismal fourth place in Iowa, Biden’s national polling has begun to slip, too.

The key insight of Biden and his supporters early on was that the Democratic Party isn’t truly ­defined by the woke-most voices on Twitter, and there are still plenty of relatively moderate Democratic voters. This didn’t mean, though, that Biden was best-suited to represent them.

The establishment’s 0-2 record backing Clinton and Biden is why, if it is forced to mount a “Stop Bernie” campaign, it won’t have much credibility. Why are these people — who insisted on the weakest general-election candidate in decades and then boosted a candidate whose performance has fluctuated in a band between woeful and lackluster — to be trusted to tell voters who is a strong candidate or not?

Certainly, the Democratic experience the last two elections, coupled with Trump’s shocking 2016 victory, suggests that party insiders know less about electability than they think they do. They are naturally inclined toward the safe and the familiar, when, as the great Zionist Theodore Herzl observed, “it is the simple and fantastic which leads men.”

That’s always going to be uncomfortable compared to the candidate of experience — and of baggage and outdated assumptions.

Twitter: @RichLowry