What Super Tuesday tells us is that a lot of Democrats would rather risk losing to President Trump with Joe Biden than allow a socialist like Bernie Sanders to hijack their party.

That’s good for America, but it’s also a treacherous Hail Mary pass for the party.

The 77-year-old former vice president showed why, moments after taking the stage in Los Angeles on Tuesday night: He mistook his wife for his sister.

“They switched on me,” he tried to explain.

He went on to give a good speech about healing the nation, and dutifully kept to the script on his teleprompter.

But then a protester leaped on stage and Biden’s wife, Jill, 68, instinctively stepped between him and the lunging vegan, grabbed the woman by the wrists and shoved her away.

It was a heroic performance, but it also showed Biden’s peculiar passivity: He just stood there, not reacting, as his wife went into physical battle for him.

When the scuffle was over, he placed a protective arm on her back, but it was as if he didn’t realize what had just happened.

The truth is that anyone who has seen Biden up close knows he has some sort of cognitive impairment. He often seems bewildered, can’t remember what state he is in, if he’s running for the Senate or the presidency or even whether it’s Super Tuesday or “Super Thursday.”

On Monday, in Texas, he forgot the words of the Declaration of Independence mid-sentence, substituting “the thing” for God.

“We hold these truths to be self-evident,” he began. “All men and women created by the [pause, consternation, hands waving] go, you know, you know, the thing.”

It’s sad to see the fear in his face when he suffers these “senior moments.”

Everyone has memory lapses, but the problem for Biden is that his are all too frequent and bizarre, and the attempt to explain them away as a function of his childhood stutter are only a temporary diversion.

These are not just the tall tales and malapropisms that long have been part of the Biden persona. It’s something new.

We know he underwent surgery for two brain aneurysms in 1988, although his surgeon, Dr. Neal Kassell, recently said Biden did not suffer any brain damage “whatsoever.”

But the kindness that has suppressed any honest discussion about Biden’s mental acuity will be swept away if he wins the nomination.

The campaign can’t keep him in witness protection forever. At some point, he’ll be caught without the teleprompter, and an off-the-cuff Joe is a ticking time bomb.

As soon as voters saw him up close and personal in Iowa and New Hampshire, the light switched on for them that the lights weren’t all on with him.

That’s when his poll numbers started plunging.

He was low energy and frequently befuddled. If he were your grandfather, you’d take away the car keys. His aides hauled around a teleprompter to small gatherings so he safely could deliver a stump speech that any other candidate could do in their sleep, but even then, he strayed off course.

It got to the point where Democratic insiders in New Hampshire started a story that Biden’s heart wasn’t in it, that he was running only to fulfill a promise he had made to his dying son, Beau.

To be fair, his team had always said to wait until the South Carolina primary, where his appeal to black voters would kick in.

Sure enough, 72 hours after a resounding victory there, he defied even the most optimistic expectations with his Super Tuesday triumph at the expense of Sen. Bernie Sanders. Now he’s the “Comeback Kid” with “Joementum.”

He won states in which he had no campaign offices, no money, and which he barely visited. That’s impressive, but what it also tells you is that a lot of Democrats went for the “idea” of Biden: the decent, compassionate, moderate candidate they desperately want to believe exists.

They didn’t want a revolution or free stuff or an autocratic billionaire. So they closed their eyes and signed up for the Biden mirage.

But if, by some miracle he does happen to become president, how would he fare dealing with Russian autocrat Vladimir Putin or Chinese President Xi Jinping? Would he have the bandwidth to manage war and the economy at a time of global turmoil?

How would he cope with 14-hour days, having to jump off Air Force One straight into the heat of India for meetings and outdoor rallies, and then race back to handle a pandemic?

Jill obviously feels he needs protecting, even from small vegans. How do we know that if Biden became president, he wouldn’t be a puppet manipulated by others?

A couple of weeks ago, he promised not to seek a second term “if anything changed in my health, making it incapable for me to fully exert all the energy and mental acuity that was needed.”

Who votes for a president who admits he doesn’t have the juice for two terms?

The Democratic-friendly media may nurse him through the campaign, but President Trump will be merciless to “Sleepy Joe.”

The party machine knows this. They are throwing him to the wolves.

It’s cruel to him and it’s a dirty trick to play on voters.

Schu’s shame

What a disgraceful fraud Chuck Schumer is, telling Trump-appointed Supreme Court Justices Neil Gorsuch and Brett Kavanaugh that they will “pay the price” unless they do what he wants.

If anyone else threatened a judge, they’d be arrested.

“You have released the whirlwind,” he said, directing the comment at the justices as he addressed protesters in front of the court as it considers a Louisiana law requiring abortion doctors to have admitting privileges at a hospital within 30 miles of the clinic.

But it’s a good law for women. You just have to remember abortionist butcher Kermit Gosnell, a k a “America’s Biggest Serial Killer,” to know why health authorities should not give free rein to abortion clinics.

Show some grace, Liz

If Elizabeth Warren can’t win the votes of the people who know her best, in her home state of Massachusetts, she’s finished. It’s a lame excuse from her supporters that she can’t quit the presidential race because that would disillusion little girls who look up to her as a role model. No, the message she sends them by clinging on is that humility, grace and self-knowledge are for suckers.