Did a bad photo op change history? No. But the image of Michael Dukakis riding around in a tank during the 1988 presidential campaign tells us a lot about how campaigns do and don’t work. In “Backfire: How To Destroy A Presidential Candidate,” a short documentary from FiveThirtyEight and ESPN Films, director Jason Reid looks back at how Vice President George H.W. Bush overtook Dukakis in the polls and won the election, and considers a basic question: Do campaigns have defining moments?