Forty years ago Friday, in the jungles of Guyana, the late Jim Jones set a record for the mass murder of American citizens that held until Sept. 11, 2001.

In his eye-opening and immensely readable new book “Cult City,” Daniel J. Flynn reminds us that Jones was less an aberration than the advance guard of the left’s long march through the culture.

In the book, Flynn appropriately pairs Jones’ story with that of gay political icon Harvey Milk, a Jones supporter right up until the end. For Milk that end came nine days after Jones’ when he and San Francisco Mayor George Moscone were murdered in City Hall.

Among the traits Jones and Milk shared, beyond hustling underage males, was the now-routine public shaming of individuals who fail to embrace the left’s shifting agenda.

Both men had also mastered the reductio ad Hitlerum long before it became a staple of the progressive tool kit. “We don’t need Uncle Toms to lead us to the gas chamber,” said Milk on one occasion, showing a precocious mixing of shaming metaphors.

Not surprisingly, it was while at college – Indiana U – that Jim Jones got his first injection of Marx, and he was hooked from the beginning.

Given that promoting communism in 1950s Indianapolis held about as much promise as promoting traditional marriage in San Francisco, Jones took another tack.

“I decided how can I demonstrate my Marxism,” he would recount years later. “The thought was ‘infiltrate the church.'”

Jones’ strategy was a proven winner in Communist circles: exploit America’s Achilles heel, racial injustice. This he did as well, recruiting hundreds of Christian blacks and then subtly shifting their focus from Jesus to Marx, all the while reinforcing their fear of white America.

By 1970, the Peoples Temple had shed all but the illusion of Christianity. By 1973, after aggressive recruiting in black neighborhoods nationwide, the Peoples Temple boasted some 2,500 members, most of them in San Francisco.

Better still, they voted as if with one voice, Jones’. And not only did they vote en bloc, they rang doorbells and made phone calls and hung posters en bloc. “He is virtually able to produce physically more people than anyone I know,” said future San Francisco Mayor Willie Brown.

Given their affection for independent thinkers – and so many of them in one place! – the city’s progressive politicians wooed Jones like a Southern belle.

From Milk to Brown to Walter Mondale to Rosalynn Carter, Jimmy’s wife, they all came a courting. “I figured if these people – if anybody should know, they should know,” testified one black survivor as to why he stuck with Jones.

After taking office as San Francisco mayor in 1976, Moscone repaid Jones by appointing him to the Human Rights Commission and then to the chairmanship of the San Francisco Housing Authority. That same year, the Los Angeles Times named Jones “the humanitarian of the year.”

In 1974, Jones leased 3,000 acres of land in a Guyana jungle and began construction of a commune called the Peoples Temple Agricultural Project. Hundreds of his followers were dispatched there to work. What they discovered was a South American gulag equal parts Werner Erhard and Pol Pot.

The buzz about Jonestown persuaded Rep. Leo Ryan, a vestigial Democrat who cared more about people than “social justice,” to check the place out.

When Jones found out about Ryan’s impending visit, he resorted to the ultimate Democratic gambit – race baiting. He denounced Ryan as someone who had “voted sharply in racist terms and fascist terms” and began rehearsing his people for “White Night,” the night when Ryan and other evil white people would come to kill them.

In preparation for visits from outsiders, Jones had earlier issued proclamation No. 75: “Give your original name when guest is here – do not use your socialist names such as Lenin, Che Guevara, etc. …”

On his visit Ryan quickly saw through the subterfuge. When he attempted to fly back to civilization with some escapees, a Jonestown security team murdered him and four others on the runway.

That night Jones put his well-drilled minions through a “White Night” exercise. They had been through this before, drinking the proverbial Kool-Aid and surviving. This time the drink was heavily laced with valium and cyanide.

Everyone who drank it died. Those who refused to drink it were injected with it. As to Jones, he shot himself.

At the time, Milk was pioneering a softball version of what Jones did, a strategy that has become the Democratic norm: embrace minorities, alert a partisan media to the embrace, woo the minorities for their support, reward them for it with various giveaways, and scare them with tales of racist, sexist, homophobic whites.

Then, when all goes to hell, as it inevitably does, blame Donald Trump or some evil “other” and so deform the story in the retelling that future generations learn nothing.

Today, we make jokes about “Kool-Aid” drinkers and write the Jonestown misadventure off to some bizarre suicide cult.

The fact is, however, that 3-year-olds typically don’t know how to commit suicide. Authorities dumped the bodies of more than 250 of the Jonestown children, almost all of them black, into a mass grave in Oakland’s Evergreen Cemetery.

There they lie to this day, unsung and un-mourned – because their death serves no useful political purpose.

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