At a hearing in Federal District Court in Washington, the man, Peter Schwartz, 49, joined a growing list of people charged with assaulting the police on that day who have received stiff sentences.
Until now, the longest sentence in a Jan. 6 case had been the 10-year term given to Thomas Webster, a former New York City police officer who was found guilty last year of swinging a metal flagpole at an officer at the Capitol.
The sentence could presage more long prison terms to come.
The prosecutors said holding Mr. Rhodes accountable at his sentencing hearing, scheduled for May 24, would be essential to preserving American democracy.
His punishment, they said, could help decide whether “Jan.