It didn’t start with Donald Trump.

That’s the thesis of Matthew Continetti’s new book exploring the darker recesses of the American right and how they contributed to the rise of the 45th president.

In “The Right: The Hundred Year War for American Conservatism”, Mr Continetti details the oft-forgotten forerunners of Trumpism: Father Charles Coughlin, the pro-Nazi “radio priest” of the 1930s; ace-aviator Charles Lindbergh, who went on to lead the isolationist “America First” movement; the Cold War red-baiter, Senator Joseph McCarthy; George Wallace, who rode the “white backlash” to political success in the civil rights era; and Pat Buchanan, the right-wing journalist/White House communications chief whose effort to deny George HW Bush renomination in 1992 helped end a streak of Republican presidential election victories.

“These tribunes of discontent,” says Continetti “have succumbed to conspiracy theories, racism, and anti-Semitism. They have flirted with violence. They have played footsie with autocracy.”

But Mr Buchanan – who 30 years ago this month declared “a religious war going on in our country for the soul of America” – is one of the few of Mr Trump’s forerunners who lived to see, and celebrate, their contribution to the MAGA movement.

Mr Buchanan’s infamous cultural war speech to the Republican convention – which berated gay rights, feminism and secularism – marked a sharp break with the sunny conservatism of Ronald Reagan and drove many moderate voters into the arms of the Democrats. As the columnist Molly Ivins quipped: “Many people did not care for Pat Buchanan's speech; it probably sounded better in the original German.”

In reality, though, there is little amusing about Mr Buchanan’s baleful contribution to the degeneration of the American right.

An alum of the Nixon and Reagan White Houses, by the early 1990s Mr Buchanan had become what one observer termed: “the most visible and maybe the most important conservative in America”, with shows on CNN and NBC and columns syndicated to 180 newspapers.

In December 1991, Mr Buchanan announced he would challenge George HW Bush for the Republican party nomination. Under the slogan “Make America First Again”, he attacked the “globalist” Bush agenda, presented himself as an anti-establishment outsider and backed protectionism, isolationism and a closed-door immigration policy. Sound familiar?

While failing to unseat the president, his campaign drew a hugely symbolic 37 per cent in the much-watched New Hampshire primary and gained nearly one-quarter of the vote nationwide. Having helped to torpedo HW Bush, Mr Buchanan ran again for the Republican nomination four years later, won four primaries and, as in 1992, managed to amass around three million votes.

But what was most remarkable about Mr Buchanan’s performance, however, was that he achieved it amid a welter of allegations about what the ADL termed a “disturbing pattern of baiting Jews and attacking Israel”.

Indeed, in the week he declared his candidacy, Newsweek magazine ran a feature headlined: “Is Pat Buchanan Antisemitic?”, while the influential conservative National Review ran a 40,000-word essay on antisemitism among intellectuals. Its author, the magazine’s legendary founding editor, William Buckley, concluded: “I find it impossible to defend Pat Buchanan against the charge that what he did and said … during the period under examination amounted to anti-Semitism.”

Although Mr Buckley’s essay focused on remarks made publicly by Mr Buchanan in the run-up to the 1991 Gulf War, his problematic relationship with American Jews long preceded Saddam Hussein’s invasion of Kuwait.

An early obsession of Mr Buchanan’s was what he termed in 1983 an “endless search for Nazi war criminals”. What was the purpose, he asked, of “all this wallowing in the atrocities of a dead regime” when the plight of present-day victims of communism allegedly elicited “scarcely a peep of protest”.

Moreover, as Newsweek detailed, Mr Buchanan engaged in a conspicuously “long battle with Nazi-hunters”, controversially weighing into the cases of Nazis like John Demjanjuk, Klaus Barbie, rocket scientist Arthur Randolph and Karl Linnas, who was later convicted of atrocities in Estonia. (Mr Buchanan’s defence was that the alleged war criminals were being denied due process and pursued as part of a “devil’s bargain” between the Justice Department and the KGB. He has denied accusations of antisemitism and claimed he has been targeted by pro-Israel groups).

In his seeming effort to defend Mr Demjanjuk, who he later termed an “American Dreyfus”, Mr Buchanan even suggested in a March 1990 column that hundreds of thousands of Jews could not have been killed at Treblinka by diesel engine exhaust fed into the gas chamber.

But it was Mr Buchanan’s charge in the summer of 1990 that Capitol Hill was “Israeli occupied territory” – which was swiftly followed by the claim that “there are only two groups that are beating the drums for war in the Middle East—the Israeli Defense Ministry and its amen corner in the United States” – which set off a political firestorm.

“We are not dealing here with country-club anti-Semitism but with the blood libel that often grows out of it: Jews are not like us but are others, with alien loyalties for which they will sacrifice the lives of Americans,” wrote Abe Rosenthal, a former executive editor of the paper, in the New York Times.

Mr Buchanan, of course, was unrepentant, claiming that he was the true victim, and accusing Mr Rosenthal and leading Jewish organisations of using “the branding iron wielded by a tiny clique, to burn horribly heretics from their agreed-upon political orthodoxy”.

And, indeed, over the years Mr Buchanan has doubled-down on this grim record. Throughout George W. Bush’s time in the White House he repeatedly claimed that the president’s foreign policies were being pursued at the behest of Israel. “What these neoconservatives seek is to conscript American blood to make the world safe for Israel,” he claimed as the Iraq war commenced in 2003.

Mr Buchanan’s dismissal of accusations of peddling antisemitic tropes might have held more water if he hadn’t later gone on to suggest: “If you want to know ethnicity and power in the United States Senate, 13 members of the Senate are Jewish folks who are from 2 percent of the population.” He similarly noted in 2010 that if President Obama’s nominee, Elena Kagan, was confirmed, one-third of the Supreme Court would be Jews.

The secret to Mr Buchanan’s journalistic success, the liberal journalist Eric Alterman claimed, was the commentator’s “ability to conduct his holy war in a huggable fashion”, playing the part of the “tough Irish cop with twinkly eyes”.

Mr Buchanan did, however, run out of road in 2012 when he was dropped by MSNBC after the publication of a book in which he claimed that, thanks to increasing diversity, America was “disintegrating, ethnically, culturally, morally, [and] politically”.

But redemption was soon at hand. The words for which Mr Buchanan was knocked off his pundit’s pedestal would soon find expression in the Oval Office, albeit in a more strident and less polished and intellectually coherent form.

The rhetoric first deployed by Mr Buchanan 25 years earlier, Tim Alberta wrote in Politico magazine shortly after Mr Trump took office, “not only provided a template for Trump’s campaign, but laid the foundation for its eventual success … Buchanan effectively weakened the party’s defenses, allowing a more forceful messenger with better timing to finish the insurrection he started back in 1991. All the ideas that seemed original to Trump’s campaign could, in fact, be attributed to Buchanan”.

Indeed, a description of Mr Buchanan’s campaign penned by the late Charles Krauthammer in spring 1992 – “the anti-intellectualism, the ersatz populism  … the paranoia, nativism, authoritarianism, ethnic and class resentment” – now reads like a premonition of Mr Trump’s rather more successful bid for the presidency in 2016.

Mr Trump, the self-proclaimed “greatest friend of Israel”, appeared to have sheared off the rougher edges of Mr Buchanan’s rhetoric about Jews and the Jewish state. Furthermore, coupled with his recognition of Jerusalem as Israel’s capital, the Abraham Accords represent the stand-out achievement of Mr Trump’s otherwise dismal foreign policy record.

However, the former president’s wooing of far-right antisemites paints an altogether more troubling picture. In the closing days of the 2016 campaign, for instance, Mr Trump ran an ad attacking the “global power structure” that has “robbed our working class” and “stripped our country of its wealth”. It was illustrated by the images of three prominent Jews. He later infamously called the neo-Nazis who chanted “the Jews will not replace us” at Charlottesville “very fine people” saying that there was two sides to the story.

And, both in and out of office, Mr Trump has invoked antisemitic tropes about Jewish money and “control” of politicians and the media, while also suggesting that American Jews who vote Democrat aren’t loyal to Israel, while describing Benjamin Netanyahu as “your prime minister” in an address to the Republican Jewish Coalition.

“In the end, Trump is amoral,” suggested the New Yorker’s David Remnick last December. “If an appeal to bigotry wins him support, if it is in the interest of his personal power and fortunes, he will make those appeals without hesitation or shame.”

Or, as Michael Kinsley, a liberal Jewish journalist with whom Mr Buchanan clashed frequently on TV but who also defended his former colleague against charges of antisemitism, succinctly put it to Politico: “Pat might be a nut, but he’s not a con man. Trump is both a nut and a con man.”