I was a Dem operative for the Democrat Majority Caucus of the California Legislature way back in the late 70s/early 80s. Believe me, you have no idea what a-holes politicians are until you have worked for them. I am betting Fetterman's inability to retain staff has more to do with his personality, and less to do with his policy positions.
And BTW, it is politicians of both parties. They all act like spoiled, petulant children. Most of them win election by sucking up to party leaders, then they hate themselves for being sycophantic leeches, so they take it out on their staff.
I saw the same thing when I was in grad school. If a professor had a hard time when he was a student, his resentment led him to abuse students himself. In politics, this is amplified because politicians, unlike profs, have real power over people.