The highest-profile prosecution to stem from the January 6 attack on the US Capitol gets under way on Monday in Washington DC, where the founder and four members of the far-right Oath Keepers group will stand trial in federal court on civil war-era charges of seditious conspiracy.

It’s a high-stakes trial for the US government, which will attempt to prove that Stewart Rhodes and his associates spent weeks marshaling members of the group to prepare to use violence to deny the certification of the 2016 election and keep Donald Trump in the White House.

The five charged with seditious conspiracy – Rhodes, Kelly Meggs, Jessica Watkins, Kenneth Harrelson and Thomas Caldwell – face 20 years in prison if convicted. Two of the 11 people indicted in the case – Brian Ulrich and Joshua James – have pleaded guilty to seditious conspiracy. The remaining four will be tried separately.

Court documents show that the Oath Keepers – described by the government as “a large but loosely organized collection of individuals, some of whom are associated with militias” that “explicitly focus on recruiting current and former military, law enforcement and first-responder personnel” – were among the individuals and groups who forcibly entered the Capitol.

Before the rally, the group had allegedly discussed paramilitary training and setting up a “quick reaction force” at a Virginia hotel that could get weapons into Washington quickly if required and had equipped themselves with thousands of dollars’ worth of guns and tactical gear, including a shotgun, scope, sights and night-vision devices.

But while Rhodes, who established the Oath Keepers in 2009, is not accused of entering the Capitol, cellphone records allegedly show he was communicating with Oath Keepers who had and was seen with members of the group afterwards.

The trial, which is expected to last about five weeks, comes as at least 919 people have been arrested and charged with crimes relating to what many, before and after the events of January 6, have called an attempted coup d’etat. More than 400 have pleaded guilty or been convicted at trial.

But the trial comes with risks for the government, which has not invoked seditious conspiracy laws since failing to successfully prosecute members of the far-right Hutaree militia in Michigan in 2010 in a case that was ultimately dismissed for insufficient evidence.

“Americans should be wary of government’s stretching ‘sedition’ charges in ways that might set troubling precedents for a US administration,” said Jim Sleeper, former professor of political science at Yale University.

At the same time, he says, “the Oath Keepers’ and their leadership’s well-documented record of excess – and Merrick Garland’s Department of Justice record of discretion and indeed of caution – incline me to trust this use of the act.”

According to attorney Bill Swor, who defended the Hutaree group, the circumstances are observably different. In that case, he says, there was no plan and no action was taken. In this, there appears to be evidence that several of the alleged conspirators broke into the Capitol and delayed Congress’s certification of the electoral college count.

“Taking the government at their claim that these individuals were acting to disrupt or prevent Congress from discharging its constitutional duty is a significant difference,” he said.

“In our case there was a vague assertion that our clients were planning a hostile, violent attack. But government witnesses testified that there was no specific plan and this was just talk and preparation, not against the government but against the forces of the antichrist who would be expressed in … an invading force of United Nations blue helmets.

“There was no suggestion that our clients had undertaken any steps to do anything beyond ‘training’ in their immediate geographical area,” Swor adds.

In the government’s case against the Oath Keepers, members traveled from across the US with a specific plan, accumulated firearms and brought them to suburban Washington and would have transported them to the seat of government if necessary. “Not only do you have the express purpose but acts taken in preparation to execute a plan,” Swor added.

Rhodes’s attorneys have said their defense will focus on their client’s belief that Trump was going to invoke the Insurrection Act and call up a militia to support his attempt to stay in power. His actions, then, were not seditious because they were only designed in anticipation of what they believed would soon become lawful.

“What the government contends was a conspiracy to oppose United States laws was actually lobbying and preparation for the President to utilize a United States law to take lawful action,” Rhodes’s attorneys, James Lee Bright and Phillip Linder, said in a court filing.

Other defendants have argued that they traveled to Washington to provide security for VIPs or rally-goers from anti-fascist protesters, or antifa.

According to the government, Rhodes sent a message to an Oath Keepers chat two days after the presidential election to reject the election results. “We aren’t getting through this without a civil war,” Rhodes allegedly wrote. “Too late for that. Prepare your mind, body, spirit.”

Court documents further allege that Rhodes spearheaded an online meeting with members of the group in which he outlined a plan to stop the transfer of power to Joe Biden. After that, prosecutors say, members of the alleged conspiracy began recruiting, training and coordinating their activities.

A month later, on 11 December, Rhodes allegedly posted on a group chat that if Biden were to take office, “it will be a bloody and desperate fight. We are going to have a fight. That can’t be avoided.”

The day before certification on 5 January, the alleged conspirators transported their weapons to Washington. The following morning, Rhodes messaged: “We will have several well equipped QRFs outside DC. And there are many, many others, from other groups, who will be watching and waiting on the outside in case of worst case scenarios.”

However the Oath Keepers trial is resolved, Swor says, the case may serve to set standards around where the individual rights to speak out and protest contravene laws protecting the functioning of government. In the case of the Sedition Act, the law was passed to curb the activities of the Ku Klux Klan, which opposed laws protecting African Americans and Catholics after the US civil war.

If nothing else, the contrast between the Hutaree and Oath Keeper cases could establish “clear, bright lines and what is, and what is not, sedition,” Swor says. “In the Hutaree case, the goal was to be prepared to respond to an invasion or defend the government. In the Oath Keepers case, the government’s theory is that these people planned and took action, and that the purpose of their activity was to prevent the government from acting.”