There are dates that reach. July 20 has, on at least three occasions across the twentieth century, been the date on which human beings attempted something they were not certain they could survive — and found out, in very different ways, what certainty was worth. On July 20, 1944, Colonel Claus von Stauffenberg placed a briefcase containing a kilogram of plastic explosive under a table in the Wolf’s Lair, Adolf Hitler’s field headquarters in East Prussia.