On that note, Tuesday was an exercise in déjà vu for both the activist and the company involved in what might be the year’s strangest activist campaign. Greenlight Capital, a $9 billion fund run by investment soothsayer and poker player David Einhorn, has borrowed heavily from a thesis it pushed at Apple four years ago to launch an ambitious campaign for change at General Motors. For the storied automaker, that makes two major activist campaigns since it emerged from bankruptcy following the financial crisis. Not surprisingly, both sides were able to issue detailed presentations within a few days of private...