As angry supporters of President Donald Trump stormed the US Capitol, ready to smash through windows and beat police officers, Oath Keepers founder Stewart Rhodes extolled them as patriots and harked back to the battle that kicked off the American revolutionary war.

“Next comes our Lexington,” Rhodes told his fellow far-right extremists in a message on 6 January 2021. “It’s coming.”

Jurors will begin weighing his words and actions on Tuesday, after nearly two months of testimony and argument in the criminal trial of Rhodes and four codefendants. Final defense arguments wrapped up late Monday.

Hundreds of people have been convicted in the attack that left dozens of officers injured, sent lawmakers running for their lives and shook the foundations of American democracy. Now jurors in the case against Rhodes and four associates will decide, for the first time, whether the actions of any January 6 defendants amount to seditious conspiracy – a rarely used charge that carries both significant prison time and political weight.

The jury’s verdict may well address the false notion that the 2020 presidential election was stolen, coming soon after 2022 midterm results in which voters rejected Trump’s chosen Republican candidates who supported his baseless claims of fraud. The outcome could also shape the future of the justice department’s massive and costly prosecution of the insurrection that some conservatives have sought to portray as politically motivated.

Failure to secure a seditious conspiracy conviction could spell trouble for another high-profile trial beginning next month of former Proud Boys national chairman Enrique Tarrio and other leaders of that extremist group. The justice department’s January 6 probe has also expanded beyond those who attacked the Capitol to focus on others linked to Trump’s efforts to overturn the election.

In the Oath Keepers trial, prosecutors built their case using dozens of encrypted messages sent in the weeks leading up to January 6. They show Rhodes rallying his followers to fight to defend Trump and warning they might need to “rise up in insurrection”.

“We aren’t getting through this without a civil war. Prepare your mind, body and spirit,” he wrote shortly after the 2020 election.

Three defendants, including Rhodes, took the witness stand to testify in their defense – a move generally seen by defense lawyers as a last-resort option because it tends to do more harm than good. On the witness stand, Rhodes, of Granbury, Texas, and his associates – Thomas Caldwell of Berryville, Virginia, and Jessica Watkins, of Woodstock, Ohio – sought to downplay their actions, but struggled when pressed by prosecutors to explain their violent messages.

The others on trial are Kelly Meggs of Dunnellon, Florida, and Kenneth Harrelson of Titusville, Florida. Seditious conspiracy carries up to 20 years behind bars, and all five defendants also face other felony charges. They would be the first people convicted of seditious conspiracy at trial since the 1995 prosecution of Islamic militants who plotted to bomb New York City landmarks.

The trial unfolding in Washington’s federal court – less than a mile from the Capitol – has provided a window into the ways in which Rhodes mobilized his group and later tried to reach Trump.

But while authorities combed through thousands of messages sent by Rhodes and his codefendants, none specifically spelled out a plan to attack the Capitol itself. Defense attorneys emphasized that fact throughout the trial in arguing that Oath Keepers who did enter the Capitol were swept up in a spontaneous outpouring of election-fueled rage rather than acting as part of a plot.

Jurors never heard from three other Oath Keepers who have pleaded guilty to seditious conspiracy.

Over two days on the witness stand, a seemingly relaxed Rhodes told jurors there was no Capitol attack plan. He said he didn’t have anything to do with the guns some Oath Keepers had stashed at a Virginia hotel that prosecutors say served as the base for “quick reaction force” teams ready to ferry an arsenal of weapons across the Potomac River if necessary. The weapons were never deployed.

Rhodes, a Yale Law School graduate and former Army paratrooper, said his followers were “stupid” for going inside. Rhodes, who was in a hotel room when he found out rioters were storming the Capitol, insisted that the Oath Keepers’ only mission for the day was to provide security for Trump ally Roger Stone and other figures at events before the riot.

That message was repeated in court by others, including a man described as the Oath Keepers’ “operations leader” on January 6, who told jurors he never heard anyone discussing plans to attack the Capitol.

A government witness – an Oath Keeper cooperating with prosecutors in hopes of a lighter sentence – testified that there was an “implicit” agreement to stop Congress’s certification, but the decision to enter the building was “spontaneous”.

Prosecutors say the defense is only trying to muddy the waters in a clear-cut case. The Oath Keepers aren’t accused of entering into an agreement ahead of January 6 to storm the Capitol.

Citing the civil war-era seditious conspiracy statute, prosecutors tried to prove the Oath Keepers conspired to forcibly oppose the authority of the federal government and block the execution of laws governing the transfer of presidential power. Prosecutors must show the defendants agreed to use force – not merely advocated it – to oppose the transfer of presidential power.