He was a Democrat for six decades. Kennedy kid. Harvard liberal. Civil-liberties guy. The kind of Democrat who used to think the First Amendment applied to people he disliked. Then the party decided Israel was the original sin, Jewish self-defense was “genocide,” and the only unforgivable crime was noticing.
The party is the people who would rather lose Maine than dump a candidate with a Nazi tattoo, and would rather lose Jewish voters than dump the activists who made that trade look cheap.
If that doesn’t count as a reason to leave, then “leave” has no meaning. Dershowitz did the adult thing: he stopped pretending a funeral was a family reunion.