The threat from right wing extremism is as high now as it was at the time of the Oklahoma City bombing, experts say, and further violent attacks are likely – especially if Donald Trump fails to win reelection.

A generation after 168 people were killed and more than 680 injured in a bomb attack on the Alfred P Murrah federal building – an incident that remains the US’s deadliest domestic terror attack – the nation is once again experiencing a wave of right wing extremism.

As Oklahoma City prepares to mark the 25th anniversary, with a Covid-19 enforced streamed memorial service replacing the usual public gathering and reading of the names of victims, experts have issued a stark warning that far right extremists such as perpetrators Timothy McVeigh and Terry Nichols, remain active and energised.

Last year alone, right-wing extremists were responsible the vast majority of extremist attacks, with a much smaller number being carried out by homegrown Islamist terrorists and left wing extremists. Those incidents included the mass shooting in El Paso.

Despite attempts by Donald Trump to play down the threat of the far right, FBI director Christopher Wray, told Congress in November: “I will say that a majority of the domestic terrorism cases that we’ve investigated are motivated by some version of what you might call white supremacist violence.”

Violence on the streets of Charlottesville Show all 9 1 /9 Violence on the streets of Charlottesville Violence on the streets of Charlottesville Protesters clash and several are injured White nationalist demonstrators clash with counter demonstrators at the entrance to Lee Park in Charlottesville, Virginia. A state of emergency is declared, August 12 2017 Violence on the streets of Charlottesville Trump supporters at the protest A white nationalist demonstrator walks into Lee Park in Charlottesville, Va., Saturday, Aug. 12, 2017. Hundreds of people chanted, threw punches, hurled water bottles and unleashed chemical sprays on each other Saturday after violence erupted at a white nationalist rally in Virginia. AP Photo Violence on the streets of Charlottesville State police stand ready in riot gear Virginia State Police cordon off an area around the site where a car ran into a group of protesters after a white nationalist rally in Charlottesville, Virginia AP Photo Violence on the streets of Charlottesville Militia armed with assault rifles White nationalists, neo-Nazis and members of the 'alt-right' with body armor and combat weapons evacuate comrades who were pepper sprayed after the 'Unite the Right' rally was declared a unlawful gathering by Virginia State Police. Militia members marched through the city earlier in the day, armed with assault rifles. Getty Images Violence on the streets of Charlottesville Statue of Confederate General Robert E Lee The statue of Confederate General Robert E. Lee stands behind a crowd of hundreds of white nationalists, neo-Nazis and members of the 'alt-right' during the 'Unite the Right' rally 12 August 2017 in Charlottesville, Virginia. They are protesting the removal of the statue from Emancipation Park in the city. Getty Images Violence on the streets of Charlottesville Racial tensions sparked the violence White nationalists, neo-Nazis and members of the 'alt-right' exchange insults with counter-protesters as they attempt to guard the entrance to Lee Park during the 'Unite the Right' rally Getty Violence on the streets of Charlottesville A car plows through protesters A vehicle drives into a group of protesters demonstrating against a white nationalist rally in Charlottesville, Virginia. The incident resulted in multiple injuries, some life-threatening, and one death. AP Photo Violence on the streets of Charlottesville Rescue personnel help injured people after a car ran into a large group of protesters after an white nationalist rally in Charlottesville, Virginia AP Photo Violence on the streets of Charlottesville President Donald Trump speaks about the ongoing situation in Charlottesville, Virginia from his golf club in Bedminster, New Jersey. He spoke about "loyalty" and "healing wounds" left by decades of racism.

“1995 came in the middle of a surge of right wing extremism. And in 2020, we are in another surge of right wing extremism,” Mark Pitcavage, an expert on the US far right and a consultant to the Anti-Defamation League (ADL), a group that monitors hate crimes, told The Independent.

Mr Pitcavage said the extremists fell into two main groups – white supremacists and anti-government. After the 2008 election of Barack Obama, the nation’s first African American president, experts noticed an increase in anti-goverment activity.

The campaign and electoral victory of Mr Trump, who pitched himself as an anti-establishment immigration hardliner, gave a fresh boost to white supremacists. Anti-government groups, such as the militia movement, also supported Trump, and many threatened violence if he had lost to Hillary Clinton.

For the first three years those groups were largely quiet, but in the past year have become more active, partly as a result of so-called red flag laws that seek to control gun violence, and more recently in angry displays against anti-coronavirus orders put in place by state.

Asked if Joe Biden or another Democrat were elected president in November, whether there would be another surge in anti-government extremist and attendant violence, Mr Pitcavage said: “It’s certainly fairly likely.”

JJ MacNab, a fellow at George Washington University and another expert on extremists, has been monitoring anti-government this week protests in Michigan, Ohio and elsewhere. She said there had been a blurring between mainstream protesters and extremists, so that the thousands of protesters who gathered on the steps of the legislative buildings in the city of Lansing, included armed militia members and people waving Make America Great Again banners.

Oklahoma City bombing survivor says coronavirus triggers emotional pain not experienced in 25 years

She said the threat from right wing extremists was very much alive, and pointed to a failed terror plot in Kansas City, made public by the unsealing of court documents, that showed that 36-year Timothy Wilson, a father of four who had served in the military, was seeing to attack a hospital.

Wilson had been planning some sort of attack for at least six months, according to an FBI undercover agent, and was apparently angered enough by the coronavirus lockdown, to attack the Belton Regional Medical Centre.

According to the FBI’s affidavit, Wilson, who was shot and killed in a shoot-out last month with FBI agents, wanted “to create enough chaos to kick start a revolution”.

Asked to compare the threat posed by right wing extremists today to 25 years ago, she said: “I think social media made it bigger in terms of numbers, but social media also allows for a sense of community.

“Because these guys can kind of blow off steam to each other rather than going off on their own to do something big. It’s a mixed bag.”

She added: “The threat is alive and real, and thank god for the FBI and for informants.”

At the weekend’s memorial, survivors and city officials will seek to look forward, rather than backwards.

Bob Ross, the chairman of the Oklahoma City National Memorial and Museum Foundation, told ABC News: “Watching the show, which will reflect back on the bombing, while also very much looking forward in terms of what we can do as a community to make sure this never happens again.”

Others have echoed the need to do that. They accuse the authorities not only of failing to properly investigate those beyond the three men convicted who may have played a role, but of the nature of the threat, then and today.

Writer and journalist Andrew Gumbel is a former US correspondent for the The Independent. He is also author of Oklahoma City: What the Investigation Missed – and Why It Still Matters, which details a disturbing picture of government dysfunction and agency rivalry, something that would also be exposed by the attacks of 9/11.

“The most important lessons of the bombing were never learned because the US government was interested only in convicting McVeigh and Nichols, not in an honest reckoning of its own missteps and missed opportunities,” he said this week. “Federal law enforcement at the time managed both to underestimate the threat from the radical far right and to be paralysed by fear in the wake of Ruby Ridge or Waco – confrontations with anti-government radicals that spiralled out of control."