US political violence is surging, but talk of a civil war is exaggerated - isn’t it?

Dr Garen Wintemute used to laugh off warnings of a civil war coming to America as "crazy talk". Then the emergency room doctor in California saw the figures for gun sales.

Wintemute, who founded a centre to research firearms violence after years of treating gunshot wounds, had long observed that the rush to buy weapons came in waves, often around a presidential election. Always it fell back again.

"Then in January of 2020 gun sales took off. Just an unprecedented surge in purchasing and that surge continued," he said. "We were aware that, contrary to prior surges, this one wasn't ending. People are still buying guns like crazy."Many were buying a weapon for the first time.

Wintemute wanted answers and they stunned him. A survey for his California Firearm Violence Research Center released last month showed that half of Americans expect a civil war in the United States in the next few years. One in five thought political violence was justified in some circumstances. In addition, while almost everyone said it was important for the US to remain a democracy, about 40% said that having a strong leader was more important.

"Coupled with prior research, these findings suggest a continuing alienation from and mistrust of American democratic society and its institutions. Substantial minorities of the population endorse violence, including lethal violence, to obtain political objectives," the report concluded.

Suddenly Wintemute didn't think talk of a violent civil conflict was so crazy any more.

The doctor is quick to note that large numbers of those people expecting a civil war say it is only "somewhat likely". But half of the population even considering such a possibility reflects the failing confidence of large numbers of Americans in a system of government under assault by Donald Trump and a good part of the Republican party.

The FBI's search of Trump's Mar-a-Lago residence earlier this month for classified documents removed from the White House unleashed the latest barrage of threats of violence, this time directed at an institution widely regarded as a bastion of establishment conservatism.

The Florida senator Rick Scott likened the FBI to the Gestapo. In Ohio, the police killed an armed US navy veteran who attacked an FBI office. In Pennsylvania, a man with a history of vaccine denial was charged with threatening to "slaughter" federal agents he described as "police state scum", and compared to the Nazi SS and the Soviet secret police.

In the days after the search of Mar-a-Lago, the FBI and Department of Homeland Security warned of a surge in threats of violence against federal agents, their families and the judge who issued the search warrant. The FBI said these included calls for "civil war" and "armed rebellion".

That comes on top of a wave of threats against election workers since Trump alleged he was robbed of victory by fraud in 2020, and a sharp increase in intimidation of others in public service from school board members to librarians as well as elected politicians.

Wintemute said that the surge in violent threats is made more potent by rising weapons sales. "What happens when you take a society that is increasingly fearful for its future, increasingly polarised, increasingly angry at itself, and throw a bunch of guns into the mix?" he said.

Many Americans flinch at talk of civil war because it recalls the bloodiest conflict in their history. The threat of violent conflict in the US also looks very different from the wars once fought by guerrillas in Latin America and Africa, or during the breakup of Yugoslavia.

But Rachel Kleinfeld, a specialist in civil conflict at the Carnegie Endowment for International Peace, said that does not mean it cannot happen. "Countries with democracies and governments as strong as America's do not fall into civil war. But if our institutions weaken, the story could be different," she said.

"What most worries me right now is polling that suggests somewhere between 20% and 40% of Americans would like a strongman leader who doesn't have to follow the democratic rules. That would allow institutions to weaken and an insurgency like the Troubles in Northern Ireland could break out."

The parallel with Northern Ireland may jar but recent polling suggests it is not unwarranted. In 1973, in the midst of some of the worst years of the Troubles, one in five people in Northern Ireland agreed that "violence is a legitimate way to achieve one's goals". Half a century later, a similar proportion of Republican voters in the US say that it is "justified to use political violence to accomplish political goals".

A more complex picture emerges when the numbers are broken down, including over whether such violence is targeted against people or property. But even then Kleinfeld said the results are disturbing. "You're looking at 3 to 5 million Americans willing to harm other Americans for their political beliefs," she said.

The US has a long history of political violence and killings, including bombing campaigns by radical leftwing organisations in the 1970s and more recent attacks from the right by anti-abortion groups and white nationalists. The country's deadliest domestic terrorist attack, the 1995 bombing of the federal building in Oklahoma City that killed 168 people, was perpetrated by members of an anti-government militia.

But now the greatest threat to political stability comes from within the power structure including Republican politicians subverting the electoral system and further eroding trust in democracy.

Trump's allegation that the 2020 presidential election was stolen unleashed actual and threatened violence from the storming of the Capitol to the barrage of threats to kill election workers. The justice department set up a special taskforce to protect election officials after more than 1,000 were directly threatened over their unwillingness to declare Trump the winner in 2020. Many have quit or intend to do so before the 2024 presidential election because of "politicians' attacks on the system and stress".

Wintemute said that with the attack on election workers has come a parallel effort by Republican leaders to weight the electoral system in their favour through gerrymandering and obstacles to voting in swing states that further undermines confidence in democracy.

"One of the great ironies is that there is the false narrative that the election was rigged which is being used in order to set up a rigged election in the future," he said.

"Democrats see democracy is under threat because of authoritarianism from the right and the prospect of stolen midterms and the infrastructure that's been setting up for a stolen presidential election in 2024. For the right, it already happened. Many people in our survey say 2020 was stolen. So their point of view is that the threat has been realised. It's hard to see a good way out."

To Kleinfeld that in part explains the significant numbers of Democrats also prepared to justify political violence in certain circumstances - 13% compared with 20% of Republicans. She said that, nonetheless, actual acts of violence are almost entirely from one side.

"What that suggests is that the American people are very frustrated with our democracy, and don't think it's working. But Republicans think they can get away with violence, and it's being normalised by their leaders, whereas Democratic leaders are keeping a check on their side. But that's not to say that will be forever," she said.Underpinning all of this are America's changing demographics and the diminishing of white political power.

Wintemute's survey showed that one in three people buys into the far right "great replacement" conspiracy theory that white Americans are being supplanted by minorities - cited by the murderers of dozens of people in recent massacres from Texas to New York state. The "great replacement" theory is also regularly aired on Fox News.

Lilliana Mason, the author of Uncivil Agreement: How Politics Became Our Identity, said the election of the US's first black president, Barack Obama, in 2008 made race "a really salient issue" for many white voters.

"Then Trump said the quiet part out loud. He started using overtly racist and misogynistic language and creating a permission structure for his supporters to become much more aggressive and intentionally offensive in their rhetoric. That really encouraged not just uncivil behaviour but broke all of these social norms that we had previously considered to be sacred," she said.

Trump's embrace of white nationalist groups, such as the Proud Boys and Oath Keepers, also brought armed militias into mainstream politics, helping them to infiltrate local police forces and the military.

In December, three retired US generals said that Trumpism has infected parts of the armed forces and noted the "disturbing number of veterans and active-duty members of the military" who took part in the attack on the Capitol. They warned of the "potential for lethal chaos inside our military" if the result of 2024 presidential election is disputed.

"The potential for a total breakdown of the chain of command along partisan lines - from the top of the chain to squad level - is significant should another insurrection occur. The idea of rogue units organizing among themselves to support the 'rightful' commander in chief cannot be dismissed," they wrote

"It really does feel a pivotal moment in in American democracy," says Mason. "We're probably going to see more violence. I don't think we'll see less in the immediate future. But, ultimately, the way Americans respond to that violence will determine whether it can be calmed down or whether it spirals out of control."

Kleinfeld said she is not optimistic.

"We're getting to a point where if the Trumpist faction wins, I think we'll see sustained extremely high levels of violence for the foreseeable future. And if they lose, I think it'll be worse," she said.