The last time American Jews gave the majority of their votes to a Republican presidential candidate was precisely a century ago, when they were foolish enough to vote for Warren G. Harding.

They won’t make that same mistake in 2020 with Donald J. Trump. Certainly not after John Bolton’s new book, and not after wiser heads around the president belatedly realized his colossal insensitivity and tried to make up for it this week.

Do the words “mass incarceration” mean nothing to Trump?

Or the words “concentration camps”?

We thank John Bolton, Trump’s former national security advisor, for giving us the latest glimpse into Trump’s malignant nature. It will help continue the century-old tradition of Jewish presidential voting, unless this generation of Jews is so tone-deaf that they hear those awful phrases and fail to make the obvious genocidal connection.

Trump apparently couldn’t see that connection, but surely most people, whatever their faith, can.

Either that or the phrase “Never Again” counts for nothing, whichever religious or ethnic group is being persecuted.

As Bolton tells it in his scathing new book, “The Room Where It Happened: A White House Memoir” (Simon & Schuster), when Trump met with Chinese leader Xi Jinping last year, Xi told the president of his plans to build “a vast system of mass incarceration camps” for more than one million Uighurs and members of other largely Muslim minorities.

Former National Security
Advisor John Bolton
(Sergei Gapon/AFP/Getty Images, via JTA)

The New York Times, which nabbed an advance copy of the Baltimore-born Bolton’s 577-page tome, reported, “When Mr. Xi explained why he was building concentration camps in China, the book says, Mr. Trump said that Xi should go ahead with building the camps, which he thought was exactly the right thing to do.”

Somewhere in hell, Adolf Hitler is smiling.

Or at least he would have been. This week, the deep thinkers in the Trump administration pushed aside this president’s earlier remarks to Xi. They convinced Trump to sign into law a bill allowing him to impose sanctions on China over such mass incarcerations of religious and ethnic minorities.

The concentration camp episode is but one of many stunning revelations in Bolton’s book.

Among them is that this president did not know the United Kingdom is a nuclear power. He thought Finland is part of Russia. He thought it would be “cool” to invade Venezuela and that the South American country is “really part of the United States.”

The Ukraine connection that led to Trump’s impeachment was all true, writes Bolton. And as if it weren’t bad enough that Trump tried to blackmail war-torn Ukraine into helping his re-election bid, he tried to enlist China’s political muscle as well by encouraging Xi to increase Chinese acquisitions of soybeans and wheat to help Trump win the hearts and votes of Midwestern farmers in 2020.

Bolton uses these phrases to describe Trump: “erratic,” “foolish,” “bizarre,” “stunningly uninformed,” “unfit for office.” Each word echoes remarks made by Trump’s former chief of staff (John Kelly), his ex-defense secretary (Jame Mattis) and his former secretary of state (Rex Tillerson).

If only Bolton (and the others) had said these things months ago during the impeachment hearings, when Democrats tried to get him to testify. But go figure, he was too busy working out his $2 million book deal.

But now at least, Bolton’s opened up before November’s presidential elections.

As for the Jewish vote, Trump was never a good bet to get it. Every Democrat since Bill Clinton in 1992 has gotten at least 69 percent of that vote. Even Dems who were crushed in presidential elections — such as Adlai Stevenson, George McGovern and Michael Dukakis — have won at least 60 percent of the Jewish vote. Franklin Roosevelt and Lyndon Johnson each got 90 percent of it. Four years ago, Hillary Clinton received 71 percent.

In recent years, the heaviest percentage of the Jewish vote that’s gone to Republicans has been cast by the Orthodox. Polls say they continue to back Trump.

Perhaps Bolton’s book will give them second thoughts. Specifically, Trump’s unbridled enthusiasm for concentration camps for persons of a specific religion and ethnic group.

Does that not bring the phrase “Never Again” to mind? Do those words count for nothing beyond mere lip service?

Or do they only count if we’re talking about Jews who are the ones trapped behind barbed wire?

 A former Baltimore Sun columnist and WJZ-TV commentator, Michael Olesker is the author of six books, including “Front Stoops in the Fifties: Baltimore Legends Come of Age” (Johns Hopkins University Press).