The trial against Oath Keepers founder Stewart Rhodes and four of his associates began on Monday as the Department of Justice (DOJ) seeks to convict them on the rarely used charge of seditious conspiracy in a Washington, D.C., court.

In opening statements, Assistant U.S. Attorney Jeffrey Nestler told jurors that Rhodes and the Oath Keepers sought to capitalize on the Jan. 6, 2021, attack on the Capitol.

“Their goal was to stop by whatever means necessary the lawful transfer of presidential power, including by taking up arms against the United States government,” the attorney said, according to The Associated Press. “They concocted a plan for armed rebellion to shatter a bedrock of American democracy.”

Here’s what to know about the high-stakes trial, which could last several weeks.

Rhodes, four other leaders are charged

Rhodes, 56, from Granbury, Texas, is a former U.S. Army paratrooper who attended Yale Law School and volunteered on Republican political campaigns before 2009, when he founded the Oath Keepers, a far-right anti-government militia group.

Members of the Oath Keepers joined other supporters of former President Trump who stormed the Capitol in a bid to stop the certification of the 2020 election, the DOJ said in charging documents earlier this year.

The House select committee investigating Jan. 6 revealed over the summer that Rhodes held a secret meeting with Proud Boys leader Enrique Tarrio in a parking garage the night before the Capitol riots.

Rhodes is also accused of leading Oath Keepers members onto the Capitol grounds and directing followers to meet him in the restricted area.

Eleven Oath Keepers face seditious conspiracy charges, but on trial this week, in addition to Rhodes, are Kelly Meggs, the leader of the Florida chapter of the Oath Keepers; Kenneth Harrelson, who assisted Meggs; Thomas Caldwell, a retired U.S. Navy intelligence officer from Virginia; and Jessica Watkins, the leader of a militia group from Ohio.

Harrelson, Meggs and Watkins are among the Oath Keepers who led a stack formation up the Capitol steps and into the building on Jan. 6, according to the DOJ charges.

Seditious conspiracy charge is rooted in months of alleged planning

While more than 900 rioters have been charged and hundreds convicted in the Capitol attacks, the DOJ is attempting to convict defendants of a seditious conspiracy charge for the first time in three decades. A seditious conspiracy charge carries a maximum sentence of 20 years in prison.

The last time the DOJ secured a seditious conspiracy conviction was in 1995, when Egyptian cleric Omar Abdel-Rahman was convicted on the charge for his role in the 1993 World Trade Center bombing.

The DOJ alleges Rhodes began planning to stop the certification of the presidential election in December 2020.

According to charging documents, on Nov. 5, 2020, two days after the presidential election, Rhodes sent a message to followers on Signal that “we aren’t getting through this without a civil war.”

On Nov. 9, the DOJ alleges Rhodes held a conference call with leaders to discuss stopping the presidential transfer of power.

Communications and messaging between leaders — including Meggs, Watkins and Harrelson — involving the use of force to stop Biden’s certification continued through early January, the DOJ says.

Watkins and Meggs allegedly helped coordinate separate teams, weapons and equipment, while Caldwell organized a base of operations for the Oath Keepers at a hotel Arlington, Va., where the DOJ says the group stashed firearms.

Rhodes also spent $7,000 on night-vision equipment and weapon sights and $5,000 on firearms, equipment and ammunition, including a shotgun, according to charging documents.

After the Capitol rioters dispersed, Rhodes and other leaders continued to meet, discussing how they could keep fighting to stop the transfer of power, the Department of Justice says, and Rhodes continued to purchase equipment.

“Patriots entering their own Capitol to send a message to the traitors is NOTHING compared to what’s coming,” Rhodes allegedly wrote on Signal on Jan. 6, 2021, according to the DOJ.

Rhodes is relying on tough defense case

Rhodes is expected to argue that on Jan. 6, he and the Oath Keepers were awaiting Trump to invoke the Insurrection Act, an 1807 law that authorizes the president to call up an armed militia or the military to quell a domestic rebellion.

The defense will assert that Rhodes cannot be found guilty of seditious conspiracy because the actions he took were in preparation for Trump’s invocation of the law, although the orders never came.

James Lee Bright, an attorney for Rhodes, told The Associated Press the legal defense is an “incredibly complicated defense of theory.”

“I don’t think that it’s ever played out in this fashion in American jurisprudence,” he said.

The defense team faces a high hurdle, as it will have to prove to the jury that Rhodes and the Oath Keepers were there to defend the government and not overthrow it.

The last time the Insurrection Act was used was in 1992, when former President George H.W. Bush invoked it amid deadly rioting in Los Angeles.

The defense team will have to prove why the defendants believed the act was going to be invoked while addressing the DOJ documents showing the Oath Keepers planned for violence to stop the certification of the 2020 election.