The ninth day of the Hebrew month of Av, “Tisha B’Av,” is the darkest day on the Jewish calendar. Jews observe it by sitting on the floor, fasting and rehearsing the calamities that have shaped Jewish history: the destruction of the Temple in Jerusalem, the Crusades, the Spanish Expulsion and the Holocaust. The holiday is the annual reminder that too many chapters of the Jewish story have been written in tears. But this year, our darkest day became even darker. Tisha B’Av commemorates the tragedies of the past, but last week, the past became the present: After spending the morning...