Every now and then, the trials have veered from this normal course as defendants have taken the stand to offer unusual — and generally unsuccessful — arguments like blaming Mr. Trump for their decision to storm the Capitol. But while some of the trials have at times been dramatic, most have been relatively uneventful and largely trouble-free.

A leader of a group called the American Phoenix Project, which was founded to fight the “fear-based tyranny” of coronavirus-related restrictions, Mr. Hostetter was accused of plotting with several members of the Three Percenter militia movement to storm the Capitol and stop the certification of Mr. Trump’s defeat.

Shortly after the election, prosecutors said, Mr. Hostetter and another leader of the American Phoenix Project, Russell Taylor, began to use the group “to advocate violence” against people that “supported the 2020 election results.” At the end of November, for example, Mr. Hostetter posted a video on the group’s YouTube channel accusing those who had not challenged the results of committing treason.

“Some people at the highest level,” he said, “need to be made an example of with an execution or three.”

Prosecutors say that Mr. Hostetter and Mr. Taylor communicated with their Three Percenter co-defendants mostly through a group chat on Telegram called “California Patriots-DC Brigade.” Mr. Taylor once described the channel as being for “able bodied individuals that are going to DC on Jan. 6” and are “ready and willing to fight.”

Mr. Hostetter went to Washington on Jan. 3, 2021, prosecutors said, checking into a room at the Kimpton George. Three days later, carrying a hatchet in a backpack, he accompanied Mr. Taylor — who also had a hatchet as well as a knife and a stun baton — into a restricted area on the Capitol grounds.

In April, in a nod to the unusual nature of Mr. Hostetter’s proposed defense, Judge Lamberth severed his case from the four co-defendants who stood accused of being Three Percenters and conspiring to disrupt the certification of the election on Jan. 6. By that time, Mr. Taylor had already pleaded guilty to conspiracy charges and under a deal with the government had agreed to serve as a witness and testify against Mr. Hostetter at trial.