On the eve of a presidential-election year there is a deep-seated anger and disquiet in the United States. An opinion poll last Sunday found Americans split on which issue was their biggest worry: 36 per cent said it was a terrorist attack, 31 per cent said gun violence. Sixty per cent of Republicans said that they feared terrorism most, compared with 22 per cent of Democrats.

The poll, for MSNBC and Telemundo, was taken after the Paris attacks last month, at the same time as killings at a Colorado health clinic but before the mass shooting in San Bernardino in California.

Early on Monday morning someone tossed a pig’s head at a Philadelphia mosque from a passing pickup truck.

Later that day Donald Trump called for a "total and complete shutdown of Muslims entering the United States until our country's representatives can figure out what the hell is going on".

It wasn’t the first incendiary remark by the businessman who is topping Republican polls to be the party’s nominee in the November 2016 presidential election – he is backed by 35 per cent of party supporters – but it was certainly the most inflammatory.

Local gun stores reported a surge in sales in the wake of the murderous rampage in San Bernardino by Syed Rizwan Farook, a radicalised US-born Muslim man, and his Pakistani immigrant wife, Tashfeen Malik, which left 14 people dead.

The US is in great socioeconomic flux, and few feel sure about their financial future. Fears about jobs and the economy poll high, after violence, among the concerns that Americans express. Income inequality is at its worst since the 1920s.

The threat of jihadist attacks is adding to the fears of a population that is already scared. A poll on Thursday found that the fear of terrorism is as high as it was immediately after the 9/11 attacks. It is perhaps no coincidence that the survey, by the New York Times and CBS News, found Trump's support rising to a new level among Republican voters at the same time that 19 per cent of all Americans said that they believed terrorism to be the most important issue facing Americans.

Firestorm

Trump’s blustering attacks on Muslims, immigrants, women, black protesters,

Barack Obama

, Republican rivals, the media and anyone who crosses him have won him fans among a section of voters: white conservatives who yearn for a return to the uncomplicated, halcyon days of the 1950s and 1960s, when the United States was great.

The reality-TV star’s plan to shut Muslims out of the country in the aftermath of the Islamic State attacks in Paris and the killings in California sparked a firestorm. Rivals accused Trump of being “unhinged,” “a fascist demagogue” and “a race-baiting, xenophobic” bigot. They may be right, but these candidates have only a fraction of the almost 30 per cent support that Trump has among party supporters, putting him well ahead of the rest of the Republican field.

Trump’s anti-Muslim remarks drew cheers from a raucous crowd at a rally in South Carolina on Monday, showing that he may be able to get away with making even the most outrageous statements.

It was the latest event packed with supporters cheering along to the bombastic drumbeat of an anti-establishment outsider who revels in his capacity to shock. He has exploited the politics of fear and loathing to great effect.

David Berg, a clinical professor of psychology at Yale School of Medicine, says that Trump reflects the collective mood more than he creates it. The businessman is giving voice to the resentment of a group that Trump calls “the silent majority”, borrowing the term made famous by Richard Nixon. “Trump is tapping into something. He cannot play on our fears unless we are susceptible to that play,” says Berg.

At a time when President Obama’s cautious foreign policy is perceived as jeopardising US security and Congress is paralysed by partisan gridlock, Trump’s black-and-white, us-good-them-bad rhetoric finds willing listeners among uneducated whites living in the shadow of existential threats.

“What Trump is speaking to them about is just the sort of everyday concerns about surviving and living a fairly trauma-free life. They are not interested in the nuances of statecraft,” says Lise Van Susteren, a Washington, DC, forensic psychiatrist who sought a Democratic nomination to the US Senate for Maryland in 2005.

His appeal comes from stoking fears by exaggerating the danger and then presenting himself as the strong leader that the people crave, according to the psychotherapist Joe Burgo, author of The Narcissist You Know, a guide to disarming and coexisting with extreme narcissists.

“He gives us these decisive, even if they are simplistic, answers: bomb the shit out of them, take out the families of the terrorists,” says Burgo. “To many frightened Americans his grandiose and bombastic personality comes across as strength.”

Such voters direct their anger at Obama because they think he is weak and indecisive, refusing to tackle issues in the uncompromising black-and-white way that a President Trump supposedly would.

“People, when they are afraid, don’t like shades of grey. They don’t like indecisiveness. They want simplistic, straightforward answers that appeal to their emotions,” says Burgo.

Trump is not alone. The Texas senator Ted Cruz, a conservative firebrand who has brought chaos to the US Congress with his brand of disruptive politics, has offered equally simplistic, hard-core solutions to complex problems. He proposed a religious test for Syrian refugees, as a way of permitting Christians to enter the US and keeping Muslims out. On some issues, such as gun control and tax, Trump is in fact to the left of Cruz and other conservatives in the fearmongering race. For Cruz the strategy is paying off. He is second in the polls, tapping into the same voter sentiments that are working so well for Trump.

Burgo believes that Trump feeds on an evolutionary mindset of survival values, mobilising a good tribe against bad enemies from outside. “So when we feel an existential threat we long for a strong leader who is going to unify us and present a decisive plan of attack to annihilate the bad outside,” he says.

Anti-Irish Catholic sentiment

The practice is well tested. The American Party, also referred to as “the Know-Nothings”, mined anti-Irish Catholic sentiment in the 1840s and 1850s, claiming that new immigrants objected to republican values and were controlled by the Vatican. The Know-Nothings fanned the fire with claims of nuns kidnapping children and spiriting them off to convents.

“What that period has in common with this period is that America was changing, and people didn’t like the way it was changing,” says Ross Baker, a politics professor at Rutgers University, in New Jersey.

Van Susteren believes that Trump appeals to feelings of humiliation, whether they are caused by the idea of immigrants coming into the US and taking American jobs or by the chaos in the Middle East deriving from the oversimplified solutions to complex issues that landed the US in trouble before. Trump evokes “a possibility to restore a sense of masculinity, because he has been successful in business and he is glitzy”, she says. “People believe that if he was president that glitziness would drip down, percolate through American society and raise us all up.”

All this comes at a time when images of recent attacks are fresh in people’s minds: the scene in California, the massacre in Paris, a pregnant woman hanging on to a building pleading for help.

“The shorthand is ‘get the hell out of a shopping mall’, ‘don’t go to that rock concert’, ‘elect a guy who is going to shoot the bad guys’,” said Van Susteren. “It is a very short-term survivalist view, and Donald Trump is able to capitalise on that.”