A Florida man who was among the angry mob that entered the Senate on Jan. 6 pleaded guilty on Wednesday to a single felony count, becoming the second person so far to publicly admit wrongdoing in connection with the riot at the Capitol.

Paul A. Hodgkins, 38, of Tampa, was caught on video breaching the Senate while carrying a Trump flag. At a hearing in Federal District Court in Washington, Mr. Hodgkins pleaded guilty to the top charge in his case: obstructing an official proceeding of Congress. As part of an agreement with the government, four lesser charges were dismissed.

Under the plea agreement, the government recommended that Mr. Hodgkins, a crane operator, receive a sentence of between 15 to 21 months in prison. His case provides an early hint of the penalties that some 200 other similarly charged defendants may face if they plead guilty too.

Since Jan. 6, about 450 people from nearly every state have been charged in connection with the riot, which contributed to the deaths of five people and resulted in injuries to nearly 140 police officers. About half of those facing charges have been accused of misdemeanors — largely trespassing and disorderly conduct — and may be sentenced to little or no prison time at all.

Many more defendants are in negotiations with the government and are expected to plead guilty in the days and weeks to come. But only one other person so far, Jon Ryan Schaffer, a heavy metal musician connected to the Oath Keepers militia, has formally entered a guilty plea.