Mr. Fetterman declined to be interviewed for this story. But aides and confidantes describe his introduction to the Senate as a difficult period, filled with unfamiliar duties that are taxing for someone still in recovery: meetings with constituents, attending caucus and committee meetings, appearing in public at White House events and at the State of the Union address, as well as making appearances in Pennsylvania.The most evident disability is a neurological condition that impairs his hearing. Mr. Fetterman suffers from auditory processing issues, forcing him to rely primarily on a tablet to transcribe what is being said to him. The hearing issues are inconsistent; they often get worse when he is in a stressful or unfamiliar situation. When it’s bad, Mr. Fetterman has described it as trying to make out the muffled voice of the teacher in the “Peanuts” cartoon, whose words could never be deciphered.

For now, Mr. Fetterman is glad to have a little break from the media glare. Current and former staff members describe him as someone who has no desire to be at the center of every negotiation and who campaigned on a promise to be a solid 51st Democratic vote in the Senate supporting President Biden’s agenda.

But his adjustment to serving in the Senate has been made vastly more difficult by the strains of his recovery, which left him with a physical impairment and serious mental health challenges that have rendered the transition extraordinarily challenging — even with the accommodations that have been made to help him adapt.