It was not the sort of complaint likely to draw public sympathy, and it did not.

Alan Dershowitz, the lawyer and professor emeritus at Harvard Law School, argued in an op-ed last week for The Hill that Americans have grown increasingly intolerant of opposing political views, focusing on a call by Representative Maxine Waters to harass Trump administration officials wherever they go.

But it was a personal note in the column that soon grabbed attention.

“I never thought I would see McCarthyism come to Martha’s Vineyard, but I have,” he wrote, of the elite island enclave off Cape Cod where he is a fixture.

Mr. Dershowitz, a self-professed “liberal Democrat,” said that friends on the Vineyard had snubbed him for publicly arguing against impeaching President Trump on television talk shows and in a forthcoming book.

“For them, it is enough that what I have said about the Constitution might help Trump,” said the lawyer, known for his fierce advocacy for civil liberties and his defense of famous clients like O.J. Simpson and Claus von Bulow. “So they are shunning me and trying to ban me from their social life on Martha’s Vineyard.”