At the hearing, prosecutors read a statement from Mr. Fairlamb’s victim, who has been identified as Officer Z.B. In the statement, the officer said he still recalled the “dread and fear” of being attacked, alone, outside the Capitol on Jan. 6, calling it “the scariest day” of his career.

In court papers filed last week, prosecutors noted that Mr. Fairlamb’s menacing behavior continued after Jan. 6. Two days later, they said, he took a video of himself threatening further violence and saying, “They pulled the pin on the grenade and the blackout is coming.”

Then, after F.B.I. agents sought to interview him, prosecutors said, he wrote on social media that he would go to the Capitol again.

In his own court papers, Mr. Fairlamb’s lawyer, Harley Breite, wrote that his client had expressed “remorse” and “tremendous shame” in September when he sat down to discuss his case with prosecutors and investigators. In online posts both before and after Jan. 6, Mr. Fairlamb seemed to echo many aspects of the QAnon conspiracy theory and voiced concerns that a civil war was coming. But according to Mr. Breite, he has since come to believe that he was “duped by social media.”

While new arrests continue almost daily and show no sign of ending, the vast prosecution of the Capitol attack has started to shift toward the process of entering guilty pleas and meting out sentences. At this point, slightly more than 30 people have been sentenced — a majority for low-level crimes like disorderly conduct and illegally parading in the Capitol. Most have avoided jail time altogether, receiving penalties of home confinement or probation.

Before Mr. Fairlamb was sentenced, the stiffest punishment given to a Jan. 6 defendant was the eight-month jail term handed down in July to a Florida man, Paul Hodgkins, who breached the Senate floor with a pro-Trump banner.

On Tuesday night, prosecutors filed court papers recommending their most severe sentence yet — four years and three months in prison — for Jacob Chansley, the so-called QAnon Shaman, who pleaded guilty in September to obstructing the business of Congress by storming the Capitol shirtless, in a horned fur hat and carrying an American flag attached to a spear.