To much of the outside world, Hamas’s decision to murder hundreds of Israelis and trigger a war that has since killed many thousands of its own people looks like a historic miscalculation — one that could soon result in the destruction of Hamas itself. Hamas’s leaders, however, say that it was the result of a deliberate calculation. Ben Hubbard, the Istanbul bureau chief for The New York Times, has been reporting on their decision, and what went into it.