Trump and Vance’s Springfield smear is a microcosm of their entire campaign | Sidney Blumenthal

After Donald Trump's disastrous debate with Kamala Harris on 10 September he decided to center his campaign on a single incendiary issue: "In Springfield, they're eating the dogs. The people that came in, they're eating the cats. They're eating the pets of the people that live there."

When Trump was corrected during the debate by the ABC moderator David Muir, who pointed out that his statement about the Haitian community in the Ohio town was erroneous, he insisted it was factual. "Well," he said, "I've seen people on television, people on television say, 'My dog was taken and used for food.'" But there were no such "people on television". There were no dogs taken for food. Trump called Muir a "foolish fool", and said, "He's a guy with good hair, but not as good as it was five years ago."

Trump showed up at the debate with a new hairstyle and tint - less Liberace and brassy blond, cut a bit shorter and softer, and shaped without the stiff angular pompadour - to lend him a more youthful appearance. His hair is always a preoccupation that has in the past had priority over policy. On a visit to France, in 2018, he refused to attend a memorial service at the Aisne-Marne American cemetery of first world war soldiers near Paris in a light rain whose humidity might loosen the firm hold of his hairspray, and gave as an excuse that the fallen were "suckers" and "losers".

At the debate, he was anxiously competing with someone on the stage other than Kamala Harris. He was fixated on the hair of the younger male journalist. His narcissism exhausts him. It gives him no rest. "It was three against one," Trump said. "I was surprised at David Muir. I thought he was a high-quality person, but he is just a sleaze like the rest of them."

But Trump quickly gave up on Muir's hair to focus on the more significant issue of "eating the pets". Trump's obsession was not an absurd, spasmodic or random act. It was not an off-ramp along the winding road of his incoherent digressions. Trump homed in on the lie as a strategic necessity. Trump understood that its outrageousness would make it unforgettable and repeatable. The falsehood served to personify the fears he routinely seeks to arouse of an alien invasion. The dogs and cats substitute for his usual horror story about a young woman murdered by an immigrant in the country illegally. He moved the blood libel to lovable pets.

After the debate left him staggering into the spin room to proclaim, "It's the best debate I ever had," before confusedly retreating, Trump's imperative has been to hold on to his base. He can afford no erosion. Losing even a point might be a falling rock that starts a landslide.

Trump desperately needed to distract the national discussion away from abortion. His pre-debate charade of gyrating positions failed to beguile women voters. His charm offensive was offensive without the charm. The gender gap widened to an even greater chasm.

The day before the debate, he held a commanding lead on the economy, 10 points over Harris, 55% to 45%, in a Pew poll. But afterwards, the FT-Michigan Ross polls showed Harris with an advantage on trust in her handling of the economy by 44% to 42%, and 48% to 42% among those who watched the debate.

Trump knows in his bones that his supporters will believe anything he says. If he ever feels they will abandon him, he cannot shoot somebody on Fifth Avenue. He does not require any evidence, not even spectral, to trigger their need to demonstrate unswerving faith. Once he speaks, declaring miracles, he is certain his supporters will fall to their knees. And, mirabile dictu, a majority, 52%, say it's true that "Haitian immigrants are abducting and eating pet dogs and cats," according to a post-debate YouGov poll. Only 5% are willing to confess the heresy that it is "definitely false", while 25% are agnostically "unsure".

Trump's lie about "eating pet dogs and cats" is his best-polling lie. It polled nine points better among his supporters than his lie that "in some states it is legal to kill a baby after birth". It polled 24 points better than his lie that "public schools are providing students with sex-change operations" and 44 points better than his lie that "noise from wind turbines has been shown to cause cancer." The raw numbers dictated the emphasis of his fiction.

The illogic of his demagogy gives Trump no pause. He has railed that immigrants are stealing "Black jobs". He says the Haitians of Springfield are illegal. But they are in fact legal and of course black. They are the black people usurping the "Black jobs".

Trump knew before he uttered his lie in the debate about "eating pets" that it was untrue. The morning of the debate, according to the Wall Street Journal, Senator JD Vance of Ohio, Trump's running mate, had a staffer call the office of the Springfield city manager. "He asked point-blank, 'Are the rumors true of pets being taken and eaten?'" that official, Bryan Heck, told the Journal. "I told him no. There was no verifiable evidence or reports to show this was true. I told them these claims were baseless."

Rather than debunk the rumor he had been informed was untrue, Vance spread the falsehood immediately. "Reports now show that people have had their pets abducted and eaten by people who shouldn't be in this country. Where is our border czar?" he tweeted, pinning the blame for the presence of the Haitian community, which had settled in the town a decade earlier, on Harris, who was incidentally not the "border czar". Within a half-hour of Vance's post, the Springfield News-Sun reported that police stated that there were no incidents of pets being stolen or eaten and that the story was "not something that's on our radar right now".

Trump repeated the lie in the debate and kept repeating it. His incitement was followed by 33 bomb threats that shut down schools, hospitals and municipal buildings in Springfield. The town's CultureFest was cancelled. Classes at Clark State College and Wittenberg University were suspended because of bomb threats. (Wittenberg was founded in 1845 at Springfield by devout German-American abolitionists. The last time classes were suspended there was for the send-off of a volunteer military company of students to fight for the Union in the civil war. When Lincoln issued the Emancipation Proclamation, the school held a day of prayer and fasting in celebration.)

"Do you denounce the bomb threats in Springfield?" a reporter asked Trump on 14 September.

"I don't know what happened with the bomb threats," Trump lied. "I know that it's been taken over by illegal migrants, and that's a terrible thing that happened." He pledged: "We will do large deportations from Springfield, Ohio. Large deportations. We're gonna get these people out." He said they would be the first to be rounded up. He would use "local law enforcement" and the national guard, despite the Posse Comitatus Act that prohibits such deployments against civilians. "Well, these aren't civilians," he claimed. "These are people that aren't legally in our country. This is an invasion of our country." "And you know," he had previously told a cheering crowd, "it's going to be a bloody story."

Trump's narrative of Springfield perfectly crystalized his nightmarish vision of the United States as "a failing nation", "going to hell" and the "misery, crime, poverty, disease and destruction to communities all across our land". It was a tale of a deindustrialized town in Middle America suddenly inundated by a horde of illegal aliens from "shithole countries", "vermin" bringing crime and disease, "not humans" murdering girls and killing pets. Long before Trump heard about Springfield, in 2017, he said, "Why do we need more Haitians? Take them out" - they "all have Aids."

Except that his story of Springfield as a parable of American decline is a myth. The town's population had fallen from 80,000 to 60,000 when the local chamber of commerce and city officials in 2014 formulated an economic development plan to bring in Haitian immigrants as crucial to revitalization. By 2020, Springfield had attracted new industries and more than 8,000 new jobs. Existing manufacturers also expanded. The New York Times, in a report, quoted Horton Hobbs, vice-president of economic development for the Greater Springfield Partnership, "It was incredible to witness the transformation of our community."

Public services, however, became strained as a result of the growth in the previously declining town. City planners had neglected to factor in their need for support from the state and federal government. So, the city manager requested federal help to deal with a housing shortage in a letter on 8 July of this year, which he copied to JD Vance. Rather than offering any help for a solution, Vance used the letter the following day in a Senate banking committee hearing with the Federal Reserve chair, Jerome Powell, to cite Springfield as an example of the problems caused by "high illegal immigration levels under the Biden administration". He was campaigning for himself to a party of one. Vance was then under consideration as Trump's running mate and his selection would be announced a week later.

Vance defended his invention of the story about "eating pets" on 15 September by insisting it was a dutiful form of constituent service. He explained it came from "firsthand accounts from my constituents". In fact, as the Wall Street Journal reported, it started with a false rumor from a Trump supporter, a woman who later discovered her missing cat, Miss Sassy Pants, was all along in the basement.

"The American media totally ignored this stuff until Donald Trump and I started talking about cat memes," Vance said. "If I have to create stories so that the American media actually pays attention to the suffering of the American people, then that's what I'm going to do." His artless admission of his compulsion to lie - "to create stories" - showed he had not yet reached the standard of shamelessness set by Trump. It's hard being a self-taught spaniel trying overnight to learn the tricks of the master. Run, Spot, run.

On 17 September, the Republican governor of Ohio, Mike DeWine, went on the PBS News Hour to tell Trump and Vance that their false claim about Springfield Haitians "needs to stop". He said that the Haitians were legal immigrants, "great workers" and "a boost to the economy". "So those comments are - about eating dogs and things - they're very hurtful."

The Trump campaign tried to deflect reproach by compounding its fictions into an amalgam of villains, projecting that it was the media that was manipulated by foreign forces to blame for distortion, that Trump and Vance had no responsibility for the atmosphere of violence, and that criticism of Trump was the cause of a deranged drifter stalking him with a semi-automatic rifle in what was presumed to be an assassination attempt.

The same day that DeWine pleaded for Trump to "stop", the Trump campaign issued a statement threading together its paranoid appeals: "The Democrat media complex spent an entire week claiming, with no evidence, that by elevating the very real, legitimate concerns of Springfield residents, President Trump and Senator Vance were somehow inciting bomb threats. That has been proven to be a complete hoax, of course - and the record must be immediately corrected. Instead of doing the bidding of foreign nations, perhaps the Fake News should take a long, hard look inside their own homes and ask how a deranged psycho - echoing their rhetoric - was inspired to try and kill the Republican nominee for president."

That day, meanwhile, Vance attempted to disentangle his statement that he needed "to create stories". "When I said - and the media always does this, they're very dishonest - when I say that I created a story, I'm talking about the media story, by focusing the press's intention on what's going on in Springfield." He was just doing his due diligence, he explained again, after his constituents told him "they'd seen something in Springfield" - the case of the missing Miss Sassy Pants. He had done nothing wrong. "Well," he said, "I think the media has a responsibility to factcheck the residents of Springfield, not lie about them." The next day Vance piped up, "I'm still going to call people illegal aliens." He meant his defiance to show to Trump he would squarely stand on the lie. Is our running mate learning?

So far, Trump's pet tactic is the representative issue of his campaign. The bizarre story of "eating pets" went from a stray unfounded rumor to Vance's social media "cat meme" to Trump's barking debating point to denunciation of the "Fake News" and the Democrats as supposed accomplices of a misfit assassin. All of these seemingly disconnected incidents are linked together by an inner logic. Its salience comes from being more than a drive-by lie. The story illuminates Trump's all-encompassing worldview. He traces the fall of the country to an ultimate source, an alien invasion that must be extirpated to prevent "corruption of the blood". The Haitian immigrants in Springfield eating the dogs and eating the cats are now his proof.