WASHINGTON (AP) — The founder of the Oath Keepers and four associates are on trial in the Capitol attack on charges that include seditious conspiracy — a rarely used Civil War-era accusation that strikes to the heart of what prosecutors say happened that day.

Stewart Rhodes and his followers are the first Jan. 6 defendants to stand trial on such a charge for what prosecutors say was not a suddenly ignited riot but a coordinated plot to stop the transfer of presidential power.

The stakes are high for the Justice Department, which hasn’t tried a seditious conspiracy case in a decade and hasn’t won a guilty verdict since the 1995 prosecution of Islamic militants who plotted to bomb New York City landmarks.

Prosecutors say Rhodes and his far-right extremist group spent weeks preparing to use violence to stop Biden from becoming president. Rhodes, a Texan, recruited members to come to Washington, amassed weapons and organized armed teams to be on standby outside the city in case they were needed, authorities say.

The plot came to a head, prosecutors say, on Jan. 6 when Oath Keepers were captured on camera shouldering their way through the mob of President Donald Trump’s supporters and storming the Capitol in military-style stack formation.

The Oath Keepers, for their part, have said their preparations, training, gear and weapons were to protect themselves against potential attacks from left-wing antifa activists, or to be ready if Trump invoked the Insurrection Act to call up a militia to support his bid to stay in power. Rhodes has said there was no plan to attack the Capitol and the members who went inside went rogue.

Jury selection started on Tuesday for the trial that is expected to last several weeks.

Here’s a look at the charge of seditious conspiracy and its history:

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WHAT IS SEDITIOUS CONSPIRACY?

The law was enacted after the Civil War to arrest Southerners who might keep fighting the U.S. government.

In order to win a seditious conspiracy case, prosecutors have to prove that two or more people conspired to “overthrow, put down or to destroy by force” the U.S. government or bring war against it, or that they plotted to use force to oppose the authority of the government or to block the execution of a law.

Rhodes, Kelly Meggs, Jessica Watkins, Kenneth Harrelson and Thomas Caldwell aren’t charged with conspiring to overthrow the government or levy war.

Instead, prosecutors charge that they conspired to forcibly oppose the authority of the federal government and forcibly block the execution of laws governing the transfer of presidential power.

Specifically, the Oath Keepers are accused of conspiring to forcibly obstruct the execution of the Electoral Count Act and the Twelfth Amendment of the Constitution, which address the counting of electoral votes.

Seditious conspiracy calls for up to up to 20 years behind bars, if convicted. Rhodes and his associates also face several other serious charges.

WHY CAN IT BE DIFFICULT TO PROVE?

The charge has rarely been brought in recent memory, and with mixed results.

It’s not enough to merely show the defendants advocated the use of force — prosecutors must show they conspired to use force. Seditious conspiracy cases are legally complex, and prosecutors are sometimes reluctant to file the charges because they can be difficult for juries to grasp.

“Juries don’t understand them, then when you want to communicate that idea to a larger audience, the public doesn’t really understand,” said Jeffrey Ian Ross, a criminologist at the University of Baltimore.

While seditious conspiracy has a broad definition, “sometimes juries want more than simple use of force against the government, because the term ‘sedition’ conjures an image of overthrowing the government,” said Barbara McQuade, who was U.S. attorney for the Eastern District of Michigan when a judge there cleared militia members of the charge in 2012.

“In the case of Jan. 6, however, because the attack against the government took place at the U.S. Capitol, while it was certifying a presidential election, even these high expectations can be met,” McQuade, now a University of Michigan Law School professor, said in an email.

Alan Rozenshtein, a professor at the University of Minnesota Law School, also said prosecutors shouldn’t have a difficult time proving seditious conspiracy in the Oath Keepers’ case.

“If this is not sedition, I don’t know what is,” he said.

WHO HAS FACED THE CHARGE BEFORE?

The last time the Justice Department tried a seditious conspiracy case was in 2010 in an alleged Michigan plot by members of the Hutaree militia to incite an uprising against the government.

A judge ordered acquittals of the sedition conspiracy charges at a 2012 trial, saying prosecutors relied too much on hateful diatribes protected by the First Amendment and didn’t, as required, prove the accused ever had detailed plans for a rebellion.

Lawyer William Swor, who represented Hutaree militia leader David Stone, has said that prosecutors in the case failed to prove that group members were “more than just talking” and were “actively planning to oppose the government.”

Stone’s “diatribes evince nothing more than his own hatred for — perhaps even desire to fight or kill — law enforcement; this is not the same as seditious conspiracy,” the judge said.

The last successful seditious conspiracy trial was in the 1995, when Egyptian cleric Sheikh Omar Abdel-Rahman and nine followers were convicted in plot to blow up the United Nations, an FBI building, and two tunnels and a bridge linking New York and New Jersey.

Abdel-Rahman, known as the “Blind Sheikh,” argued on appeal that he was never involved in planning actual attacks and his hostile rhetoric was protected free speech. He died in federal prison in 2017.

Prosecutors also secured seditious conspiracy convictions in another, now largely forgotten storming of the Capitol building in 1954. Four pro-independence Puerto Rican activists rushed the building and opened fire on the House floor, wounding several representatives.

Also, Oscar Lopez Rivera, a former leader of a Puerto Rican independence group that orchestrated a bombing campaign that left dozens of people dead or maimed in New York, Chicago, Washington and Puerto Rico in the 1970s and early 1980s, spent 35 years in prison for seditious conspiracy before President Barack Obama commuted his sentence in 2017.

And in 1988, jurors in Fort Smith, Arkansas, acquitted white supremacists charged with seditious conspiracy. The defendants were accused of plotting to overthrow the federal government and establish an all-white nation in the Pacific Northwest, and conspiring to kill a federal judge and FBI agent.

WHO FACES SIMILAR CHARGES IN THE JAN. 6 ATTACK?

A total of nine members or associates of the Oath Keepers are fighting seditious conspiracy charges. A second trial for the other Oath Keepers charged in the case is to begin at the end of November.

Three other Oath Keepers have already pleaded guilty to seditious conspiracy, are cooperating with investigators and could testify against Rhodes at trial. Rhodes’ lawyers have claimed in court documents that those Oath Keepers are lying and pleaded guilty only because they were pressured by the government and hoped to get lighter sentences.

Several members of another far-right extremist group, the Proud Boys, have also been charged with the crime, including former chairman Henry “Enrique” Tarrio. They are scheduled to stand trial in December.

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Richer reported from Boston.

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