The Party of Trump has proved itself keen to propagate any conspiracy theory, no matter how ridiculous or racist.

Well, almost any conspiracy theory.

There were the microwave ovens that surveil your every move. There were those fake jobs numbers, crafted to make President Barack Obama look good (though today, oddly, those same jobs numbers somehow make Obama look bad, according to Republicans). There were autism-causing vaccines, 3 million illegal votes, alleged murders, a pizza-parlor child-sex-slavery ring, the convoluted nonsense of QAnon.

Then Friday, Trumpkins revived a conspiracy theory that long predates our current president and has remained popular with far-right political regimes around the world: that of the International Jew.

Thousands of protesters had shown up to voice their anger over Brett Kavanaugh's imminent ascension to the country's highest court. They were, understandably, mad about Kavanaugh's record − on reproductive rights, campaign finance, executive power and other key policy concerns.

They were also mad about Kavanaugh's personal conduct − not only high-profile allegations of sexual misconduct but also his nasty, partisan attacks on Democratic senators, his claims of a vast Clintonian left-wing conspiracy and his statements under oath whose veracity has been disputed even by his friends.

But perhaps most of all, they were mad at the Republican Party.

After all, the GOP had stolen a Supreme Court seat from Obama, taken away the filibuster for Supreme Court nominees so they could push through a pick without 60?votes, and arranged for a sham FBI investigation when their pick was credibly accused of sexual assault. Some of them even mocked a woman who said she had been sexually assaulted.

Despite all this, Republican leadership somehow couldn't fathom why legions of Americans might be genuinely, grievously upset. Instead, several Republicans suggested, all those Kavanaugh protesters -- just like those phony Women's Marchers last year -- must be mercenaries. That is, they were only pretending to be mad, because they were being paid to be mad.

Not merely paid: paid by an evil, rich, foreign-born Jew.

The protesters who confronted a senator in an elevator were "Paid for by Soros and others," President Trump tweeted, in a reference to Hungarian-born American Jewish billionaire and liberal philanthropist George Soros.

Trump's tweet echoed a comment from Senate Judiciary Committee Chairman Charles E. Grassley, R-Iowa, who told a Fox Business Network host that he thought the protesters were probably paid by Soros.

Trump's personal attorney Rudolph Giuliani amplified the conspiracy theory, retweeting a comment calling Soros "the anti-Christ" and urging that his assets be frozen. Other Republican pundits also called for the survivor of Nazi-occupied Hungary to be jailed and his wealth seized.

This was not merely an attempt to scapegoat someone, anyone, for Republicans' deeply unpopular actions. It was a call for tinfoil-hatters to revive the blood libel. Soros has inherited the archetype of the International Jew who haunted the fevered dreams of Henry Ford, one of the original America Firsters. Soros has apparently shapeshifted out of "Jud Suss" and Mayer Rothschild and Shylock before him − a rootless, ruthless villain supposedly conspiring to undermine the rightful gentile order.

In any other presidency, such a dog whistle might have pierced news coverage for weeks. Instead, Republicans' anti-Semitic conspiracy-theorizing dominated headlines for barely a day.

And in fairness, why − such bigotry shock anyone at this point? Despite the Jewish faith of his daughter and son-in-law, Trump has suggested that a horde of torch-toting neo-Nazis included some "very fine people." He tweeted an anti-Semitic meme during the 2016 campaign and closed it with a TV ad pairing images of famous Jews (including Soros) with a pledge to destroy the "global power structure."

Moreover, Trump launched his political career with a bigoted conspiracy theory: that our first black president was secretly born in Kenya and was therefore illegitimate.

His paranoid crackpottery has been almost parody-defying. But these days it's not just the Alex Jones aficionados or QAnon breadcrumb-gatherers who buy into Trump's conspiracy theories. Mainstream Republicans such as Grassley do, too. Carefully reported debunking, including by The Washington Post's own fact-checking team, seems unable to shake some sense into them.

One puzzle remains, however.

Despite Republicans' willful credulity over Soros and microwaves, the one conspiracy theory they dismiss outright is the one we actually do have mounting evidence for: the conspiracy against the United States led by the Russia government, possibly with the Trump campaign's consent.

And no number of previously undisclosed contacts between Trump officials and Russian operatives, emails from Donald Trump Jr. or special-counsel indictments could convince the party faithful otherwise.

For his part, Russian President Vladimir Putin says Republicans are right to be skeptical. Whom has he blamed instead for U.S. election meddling?

Why, the Jews, of course.

Catherine Rampell's column is distributed by the Washington Post Writers Group.