A few hours after Stewart Rhodes, the leader of the Oath Keepers militia, was sentenced on Thursday to 18 years in prison for his role in a seditious conspiracy to instigate the pro-Trump violence of Jan. 6, Matthew M. Graves, the federal prosecutor who has overseen the government’s investigation of the Capitol attack, released a statement with a fact that underscored the landmark nature of the moment.
“More people were convicted of seditious conspiracy in connection with the siege of the Capitol on Jan. 6, 2021,” Mr. Graves wrote, “than any other criminal event since the statute was enacted during the Civil War.”
Nearly two and a half years after supporters of President Donald J. Trump stormed the Capitol in an effort to derail the peaceful transfer of power, Mr. Rhodes’s sentencing was the most high-profile statement of accountability yet for an episode that seems certain to occupy a dark place in American history and remains a flashpoint in American politics.
Amid the more than 1,000 criminal cases filed so far by the Justice Department against those who played a role in the attack, the prosecution of Mr. Rhodes, accused of plotting to mobilize his followers into storming the Capitol in two separate military-style “stacks,” stood out in a way that the judge who sentenced him, Amit P. Mehta, captured in court on Thursday.
“Mr. Rhodes, you are convicted of seditious conspiracy; you are a lawyer, you understand what that means,” Judge Mehta said. “Seditious conspiracy is among the most serious crimes an individual in America can commit.”
Perhaps for just that reason, sedition charges have been used only rarely over the decades, reserved for select groups of defendants who prosecutors argued uniquely threatened the government.
Sedition cases have been filed against communists, Islamic terrorists and white nationalists. Some of the cases have succeeded. But given that the statute requires prosecutors to prove an agreement to use violent force to oppose the laws or authority of the government — a difficult hurdle to jump over — many of the cases have failed.
The Jan. 6 sedition trials have all taken place just a brief walk from where the attack itself occurred — in the federal courthouse that sits only a few blocks down Constitution Avenue from the Capitol.
Scholars of political violence have widely viewed the proceedings as a major effort by the Justice Department to respond to the assault with significant indictments and to go as far as the law will allow in holding the feet of extremists to the fire and in defending the foundations of the democratic system.
There have been three separate Jan. 6 sedition trials so far, which have led to a total of 10 sedition convictions and four sedition acquittals. Four more people have pleaded guilty to sedition and avoided going to trial. All of these defendants were members of either Mr. Rhodes’s organization, the Oath Keepers, or the Proud Boys, another prominent far-right group.
But even the flurry of sedition convictions has done little to stem the larger tide of far-right radicalism. Just this month, a Texas man in thrall to Nazi ideology fatally shot eight people at an outlet mall outside of Dallas. In late April, as one of the sedition trials went to the jury, a neo-Nazi group flying a swastika flag protested a drag show in Columbus, Ohio.
At the same time, the two main Republican presidential contenders — Mr. Trump and Gov. Ron DeSantis of Florida — have both suggested that they might issue pardons to many of those convicted of taking part in the events of Jan. 6. As Mr. Rhodes himself said at his sentencing hearing, the Capitol riot defendants are increasingly viewed by many people on the right not as violent criminals, but as “patriots” and “political prisoners.”
On Friday, two Oath Keepers who were on trial with Mr. Rhodes, Jessica Watkins and Kenneth Harrelson, were given prison sentences of eight and a half years and four years, respectively — though on charges of obstructing the certification of the election, rather than sedition. Four members of the Proud Boys convicted of sedition — including their former leader, Enrique Tarrio — are scheduled to be sentenced in August with a fifth member of the group who was found guilty of lesser conspiracy counts.
During all of the trials — two that involved the Oath Keepers and one that focused on the Proud Boys — defense lawyers repeatedly claimed that prosecutors proved their case only by expanding, or even by distorting, the traditional understanding of conspiracy law.
The government, the lawyers pointed out, was never able to find a smoking gun indicating that either group had formed a clear plan or reached an explicit agreement to use force to stop the lawful transfer of power on Jan. 6. And that was despite having collected hundreds of thousands of internal text messages and turning several members of the groups into cooperating witnesses.
The lawyers also argued that the defendants who went to trial were not all that violent on Jan. 6, especially compared with other rioters. Mr. Tarrio, for instance, was 50 miles away from Washington in a Baltimore hotel room at time of the attack.
In response, prosecutors argued that all of the defendants had ties to comrades who did commit violence at the Capitol or had stashed an arsenal of weapons at the ready in Virginia. They also claimed that criminal conspiracies are rarely hatched in the light of day and that the agreements by the Oath Keepers and Proud Boys to disrupt the democratic process were reached implicitly and in an unspoken manner.
“It can be a mutual understanding reached with a wink and a nod,” Conor Mulroe, a prosecutor at the Proud Boys trial, told the jury during closing arguments.
The fact that both judges and juries in Washington have appeared to accept this expansive definition of conspiracy has given the Justice Department prominent victories in prosecuting the rioters who were on the ground on Jan. 6.
But the prosecutions have done little to resolve a different question: What legal responsibility does Mr. Trump bear for an attack intended to keep him in office despite his loss at the polls?
That issue is the focus of an investigation by Jack Smith, the special counsel appointed by Attorney General Merrick B. Garland. It is not clear what charges, if any, Mr. Smith might bring against the former president in the Jan. 6 investigation, but the outcome of the Oath Keepers and Proud Boys prosecutions has led some lawyers and legal experts to wonder if a similar approach might be used in building a sedition case against Mr. Trump.
If all it takes is a wink or a nod, the theory goes, to join conspirators in a plot to violently oppose the government’s authority, then could it be possible to construct a seditious conspiracy connecting Mr. Trump to the mob that stormed the Capitol through his incendiary speeches and tweets?
More than a year ago, Judge Mehta himself issued a ruling in three civil lawsuits that sought to hold Mr. Trump accountable for the violence of the Capitol attack, suggesting there was evidence that the former president had in fact entered into a conspiracy with the Oath Keepers and Proud Boys on Jan. 6.
More important, Judge Mehta also said that it was plausible that Mr. Trump — largely on the basis of his words alone — had aided and abetted the ordinary rioters who threatened or assaulted police officers that day.
But Alan Rozenshtein, a former Justice Department official who now teaches at the University of Minnesota Law School and has written extensively about sedition, cautioned that it could be difficult to use the Oath Keepers and Proud Boys cases as any kind of precedent to build a sedition case against Mr. Trump.
“Trump is a unique defendant in a league by himself,” Mr. Rozenshtein said. “He’s also a chaos agent and pinning down his actions in a way that shows he did any sort of planning has always been the tricky part.”
Zach Montague contributed reporting.