The current impeachment proceedings against Donald Trump are only the fourth in American history, and William Cohen has been near the center of power for three of them. First, he was a Republican member of the House Judiciary Committee in 1974, when his vote in favor of articles of impeachment helped end the Presidency of Richard Nixon. Twenty years later, as Bill Clinton’s Secretary of Defense, he had to navigate American military policy around the Lewinsky scandal. Cohen is now a Washington power-broker, and he tells The New Yorker’s Michael Luo the story of both sagas and their relation to today’s news. During Watergate, Cohen received death threats for what was perceived as his betrayal of Nixon, and he says that his chances for a Republican leadership position were “finished.” But Cohen implores his G.O.P. successors in Congress to put Constitution above party; otherwise, “this is not going to be a democracy that will be recognizable a few years from now.”