Robert Mercer seemed uncomfortable. It was 2014, and the billionaire had just stepped behind the podium to accept a lifetime achievement award at the annual meeting of the Association for Computational Linguists. Dressed in a suit and tie, he warned his audience that speaking to them for the required hour or so was “more than I typically talk in a month” and that he was no longer in their field of work. “I left IBM Research 20 years ago, and I really have not paid any attention to the world of linguistics or to IBM since then. And I can’t...