The arrest of 13 men in a plot to kidnap the governor of Michigan and "instigate a civil war" placed a fresh spotlight on the growth of armed, right-wing extremist "militias" under the administration of President Donald Trump.

The FBI says such groups constitute the greatest domestic terror threat to the country, but Trump has appeared to encourage some, leading to worries of political violence around the November 3 presidential election.

- Who are the militias?
A subculture of armed right-wing groups with varied motivations has long existed in the United States. 

After Trump came to power, many have come out of the shadows, most infamously joining the notorious 2017 Unite the Right rally in Charlottesville, Virginia, and this year protesting Covid-19 restrictions while heavily armed, and confronting anti-police and Black Lives Matter protestors.

The most prominent groups -- the Three Percenters, Oath Keepers, Proud Boys, Boogaloo Bois, and Patriot Prayer -- coalesce around anti-authority, anti-leftist and pro-gun rights ideologies. 

Some are white supremacists with ties to neo-Nazi movements; some see the police and government as authoritarian enemies; others say they are preparing for a national revolution or race war.

Some also subscribe to the QAnon movement embracing unfounded theories of a "deep state" threat to Trump and a global child-kidnapping conspiracy led by Democrats.

No one knows how many followers the groups have, but it is easily in the thousands, in all areas of the country connected by social media and encrypted messaging, according to researchers.

- Who were the people in the Michigan plot?
Many of the 13 arrested expressed support for the Boogaloo ideology, and several were members of the recently formed local Wolverine Watchmen armed militia. 

Boogaloo is an organizationless, leaderless, loosely-shaped ideology formed around gun culture and the belief of a looming war or insurrection, fought with the left, with a dictatorial government, or over race.

Some of those arrested had joined rallies this year against Michigan Governor Gretchen Whitmer's coronavirus restrictions, wearing paramilitary gear, carrying multiple weapons, and declaring their rights were being violated.

The Wolverine Watchmen regularly undertook firearms training "to prepare for the 'boogaloo', a term referencing a violent uprising against the government or impending politically-motivated civil war," said a Michigan state court filing. 

-'Domestic terror threat'
Since 2019 the FBI has said that right wing extremists, sole actors and militia groups are the country's leading domestic terror threat. They have been responsible for dozens of deaths in the past three years, compared to only a handful from Islamist extremists.

FBI director Chris Wray said in September that white supremacists are the leading violent extremism threat. But so far this year more deaths have been caused by right wing extremists who are primarily anti-authority and anti-government.

That includes the May murder of two policemen in California by a Boogaloo follower.

"It's not just a Michigan problem, it's an American problem," said Michigan Attorney General Dana Nessel. 

- Do the militias threaten the election?
Potentially, yes. President Donald Trump has repeatedly called on his followers to go to polling sites to "protect" the vote.

"I'm urging my supporters to go into the polls and watch very carefully, because that's what has to happen," Trump said during his election debate against Joe Biden in late September.

During the debate he also told the violent armed Proud Boys group to "stand by." One of the group's organizers, Joe Biggs, answered on social media: "Well sir, we're ready." 

In states that allow the open carry of firearms, there are few rules to  prevent militia groups or armed activists from descending on a voting station to watch or protest, as long as they do not directly menace voters.

But it could still be intimidating. And Wray said last week that the FBI's big fear is violent clashes between armed, ideologically motivated extremist groups on the right and left before the election. 

"Now you've got an additional level of combustible violence," he said.