Bernie Sanders’ problem isn’t the Democrat establishment, though certainly that party’s inner circle is out to screw him — and, as we’ve discussed in this space, rightly so.

But the party’s machine isn’t what’s ultimately going to finish Bernie off. It’s his own sloth and cowardice. Or perhaps it’s his dishonesty.

Look, you all already knew this, because he gave the clearest signal possible four years ago. You’ll remember when Sanders, with his opponent Hillary Clinton reeling (and becoming unelectable among general-election voters) over her email scandal, completely gacked the 2016 Democrat nomination in one indefensibly stupid quote: “I’m sick and tired of hearing about your damned emails.”

Any political candidate worth voting for would have seized on Hillary’s emails in that Democrat primary contest and pointed out that (1) hiding those emails from the public was not only illegal but also a massive breach of the public trust that disqualified her from future political office, and (2) if the email scandal wasn’t vetted in the primary, it would be vetted in the general election, and it would end up being the reason Hillary wouldn’t be able to beat Donald Trump. Both statements were unquestionably true, and if Sanders had made them like any competent candidate would have, he either would have been the nominee in 2016 or he’d be the nominee now — or he’d be in a perfect position to break the Democrat Party by leading his people out of it and into a third party with a lot better future than the Dems would have.

But he didn’t stick the knife in Hillary, just like he’s refusing to stick it in Biden when it’s patently obvious Sanders’ opponent is incompetent to continue in his campaign.

Joe Biden has always been a gaffe factory. But he’s never been as bad as he is now. Every speech he gives is replete with disqualifying blunders and indefensible statements proving he isn’t mentally fit to serve as president. And Bernie Sanders, who fancies himself as an anti-establishment revolutionary, can’t summon up the sand to point out that the establishment that is doing everything it can to screw him out of the nomination is bending and breaking the rules in favor of a doddering, senile old man who can’t form complete sentences?

Sanders is attacking Biden on Social Security. Nobody cares about Biden’s position on Social Security. It’s like Sanders’ campaign people went looking for a Broadway script and came up with “Springtime for Hitler.”

Forget about the absolute political gold Sanders can use on Biden with Ukraine and China, which are the equivalent of those emails from four years ago. We don’t even need to go there right now. Bernie could just flip over the competence card and drag in the pot, because even Biden’s voters know he can’t serve in that office.

But Bernie clearly won’t do it, and here’s a theory why: Bernie’s presidential campaigns are nothing but a grift. They’re a way to scam his donors out of enough money to buy more dachas for him and his wife.

How does the grift work? Well, the wife — she’s the one who bankrupted that college back in Burlington, you’ll remember — is, among other things, a media buyer, and Sanders’ 2016 campaign used a firm called Old Towne Media to place some $82 million in ads. Old Towne Media is, according to Patrick Howley at National File, run by a pair of Jane Sanders’ friends. With that kind of money spent so cozily, it’s not hard to imagine how a chunk of it might have been kicked back inside the family.

So far this cycle, a review of FEC data doesn’t show that firm placing any media for Bernie. The vast majority of his media buys so far this cycle, more than $14 million worth, have come out of a Denver firm called Bluewest Media. Not much is known about it, other than its CEO is a woman named Mary Wittemyer. Bluewest Media was founded in 2013, and six years later it’s making eight figures’ worth of media buys in a presidential campaign.

Sounds legit.

If what you’re really doing is scamming your donors, many if not most of whom are clueless imbeciles who will never ask where the money is going, the last thing you want to do is actually attempt to win. Running hard means attracting attention.

So if you’re dumbfounded by Bernie’s flaccidity in the face of the eminently beatable Joe Biden, consider the idea that Bernie and Jane are a modern-day Bialystock and Bloom, who have figured out that the play makes more money if it closes on opening night than if it’s a hit. That theory makes sense — though so does the theory that a guy who got kicked out of a kibbutz because he was lazy and who has never held down a real job would lack what it takes to run a successful presidential campaign.