Thirteen people have been arrested on charges of plotting to kidnap the Democrat governor of Michigan, Gretchen Whitmer, and violently overthrow the state government.
The FBI announced on Thursday that they had an informant inside the gang, who allegedly approached a Michigan militia for support in their scheme.
Joe Gasper, head of Michigan state police, said the plot and subsequent arrests were "unprecedented".
Ms Whitmer, 49, has become a lightning rod for conservatives in the deeply divided state, and her strong support for Covid-19 lockdown measures has increased the passionate antipathy many in Michigan feel towards her.
On April 17, Donald Trump tweeted: "LIBERATE MICHIGAN!"
— Donald J. Trump (@realDonaldTrump) April 17, 2020
Ms Whitmer on Thursday afternoon accused Mr Trump of issuing "a call to action" for militia groups, and said he was "complicit".
"When I put my hand on the Bible and took the oath of office 22 months ago, I knew this job would be hard," she said.
"But I'll be honest - I never could have imagined anything like this."
Ms Whitmer condemned "the disturbing recurrence of bigotry and violence".
"Just last week the president of the United States stood before the American people and refused to condemn white supremacists, like these two Michigan groups," she said.
"Stand back and stand by, he told them.
"Hate groups heard the president's words not as a rebuke, but as a rallying cry - a call to action.
"When our leaders speak, their words matter. They carry weight. When our leaders meet with, encourage, fraternise with, domestic terrorists, they legitimise their actions, and they are complicit.
"When they stoke and contribute to hate speech, they are complicit."
...today that they foiled a dangerous plot against the Governor of Michigan. Rather than say thank you, she calls me a White Supremacist—while Biden and Democrats refuse to condemn Antifa, Anarchists, Looters and Mobs that burn down Democrat run cities...
— Donald J. Trump (@realDonaldTrump) October 9, 2020
On Thursday night, Mr Trump said on Twitter she had done a "terrible job" responding to the pandemic and he did not tolerate extreme violence.
"Governor Whitmer of Michigan has done a terrible job. She locked down her state for everyone, except her husband’s boating activities," he wrote.
"The Federal Government provided tremendous help to the Great People of Michigan. My Justice Department and Federal Law Enforcement announced today that they foiled a dangerous plot against the Governor of Michigan.
"Rather than say thank you, she calls me a White Supremacist—while Biden and Democrats refuse to condemn Antifa, Anarchists, Looters and Mobs that burn down Democrat run cities.
"I do not tolerate ANY extreme violence. Defending ALL Americans, even those who oppose and attack me, is what I will always do as your President! Governor Whitmer—open up your state, open up your schools, and open up your churches!
The gang twice conducted surveillance at Ms Whitmer's summer home in the west of the state, and discussed kidnapping her to a remote location in Wisconsin to stand "trial" for treason, prior to the November election, prosecutors allege.
"Our efforts encountered elaborate plans" which were "carefully coordinated and skillfully executed," said Dana Nessel, the Michigan attorney general, at a press conference on Thursday afternoon.
Federal charges against an initial six were announced on Thursday morning, and on Thursday afternoon she said that seven more were in custody, on state charges of domestic terrorism, linked to the militia group Wolverine Watchmen.
The group was founded in 1994 by Norm Olson, a former US airforce non-commissioned officer, and claims to have more than 80 brigades in nine divisions across the state.
Experts say membership figures tend to ebb and flow according to the political climate of the day, but could number several thousand at any one time.
Training sessions involving tactical and survival role-playing and weapons use are usually held once a month, the Irish Times reported in April 2019.
The militia’s handbook claims the group is not a racist or right-wing organisation, instead welcoming everyone “regardless of the hue of their skin”, the paper said.
They are accused of attempting "to instigate a civil war and kidnap officials including the governor."
They searched for the addresses of law enforcement agents online, and made plans for overthrowing the local government.
Josh Hauxhurt, FBI assistant special agent in charge, described the 13 as "extremists" whose actions could not be tolerated.
"Several members talked about murdering 'tyrants' or 'taking' a sitting governor," an FBI agent wrote in the affidavit.
"The group decided they needed to increase their numbers and encouraged each other to talk to their neighbors and spread their message."
One of the six co-conspirators named on Thursday morning, Ty Garbin, 24, had his home raided by agents in Hartland Township late on Wednesday.
The others named in the plot are Adam Fox, Barry Croft, Kaleb Franks, Daniel Harris and Brandon Caserta.
The investigation dates to early 2020 when the FBI began to suspect through social media that individuals were discussing the violent overthrow of several state governments and law enforcement.
In June, Croft, Fox and 13 others from multiple states held a meeting in Dublin, Ohio according to the government.
Those present included an FBI confidential source who recorded the meetings. The source has been paid $8,600, the paper reported.
“The group talked about creating a society that followed the US Bill of Rights and where they could be self-sufficient,” the FBI agent wrote.
“They discussed different ways of achieving this goal from peaceful endeavors to violent actions.
"At one point, several members talked about state governments they believed were violating the U.S. Constitution, including the government of Michigan and Governor Gretchen Whitmer.
“As part of that recruitment effort, Fox reached out to a Michigan-based militia group,” the agent added.
Andrew Birge, US attorney for the Western district of Michigan, said that each of the six face up to life in prison if convicted.
Croft is a resident of Delaware; the others live in Michigan, he said.
"The alleged conspirators used operational security measures, including operating on encrypted platforms and using codewords," he said at a press conference on Thursday afternoon.
He said Fox and Croft suggested detonating devices to distract police while kidnapping her, and even located a highway bridge to blow up.
They purchased a Taser, and tested explosives.
Matthew Schneider, the US attorney for the Eastern District of Michigan, said: "All of us can disagree about politics, but those disagreements should never, ever involve violence."
They were arrested on Wednesday in eastern Michigan while meeting to discuss pooling their funds and buy tactical gear for their plot.
He said the defendants have begun to make their initial hearings.