Democrats have borrowed a medieval antisemitic conspiracy theory for their midterm campaign message.

For centuries, this evil theory has been used to persecute Jews.

The basic outline is always the same. It holds that the Jews, a small group of people from a distant land, who live differently than the rest of us, secretly control everything in our society through their money or their intelligence: We can only be free once they are stripped of their power, expelled — or eliminated.

That’s the story the imperial Russian secret service spun in the infamous forgery, “The Prococols of the Elders of Zion.” 

The “Protocols” were a staple of Nazi propaganda, and later spread throughout the Arab and Muslim worlds.

Today, they have new life — in the Democratic Party.

Democrats — most of them, anyway — are smart enough not to name “Jews” as the bad guys, so they pick on “AIPAC” instead.

Listen to the anti-AIPAC rants of Michigan Democratic Senate candidate Abdul El-Sayed. Or those of Darializa Avila Chevalier, the radical socialist who unseated the most powerful Latino in the House in last month’s New York primaries.

AIPAC is the common enemy, they insist — and they don’t even have to explain why.

Because all too many Democratic primary voters already “know” that AIPAC controls Congress, supports a supposed “genocide” of Palestinians in Gaza and dragged the United States into war against Iran.

But what is AIPAC, exactly?

It’s the American Israel Public Affairs Committee, a large and influential pro-Israel lobbying organization.

But unlike many lobbying groups on DC’s K Street, AIPAC is actually a grassroots organization. 

Its members are thousands of Americans who support Israel, of course including many Jews — but also evangelical Christians and others.

Every year, AIPAC activists gather in Washington to meet with members of Congress and their staff to ask them to support aid for Israel.

They operate in the open, not in secret.

Traditionally, AIPAC avoided giving money to candidates in elections. But after a rival outfit, lefty J Street, began backing candidates, AIPAC started a political action committee that could donate to campaigns. 

AIPAC is far from all-powerful. It failed to stop President Ronald Reagan from selling surveillance planes to Saudi Arabia; it failed to stop President Barack Obama from striking a bad nuclear deal with Iran.

But it does succeed in supporting aid to Israel — not least because Congress requires that the money be spent here at home.

So how did AIPAC become the enemy?

The effort began 20 years ago, when critics claimed, falsely, that AIPAC and the “Israel lobby” had provoked the Iraq War.

That message resonated with left-wing Democrats, already growing increasingly anti-Israel.

AIPAC tried to appease Democrats — even apologizing to Obama when AIPAC members applauded Donald Trump for criticizing him.

It didn’t help. 

Now AIPAC is demonized by Democrats on the left — even by “progressive” Jews now desperate to survive in their own party.

We know where this goes, and it’s nowhere good.