CONTEMPLATING the Clinton-Obama racial war, some Republicans were so excited you’d have thought Ronald Reagan had risen from the dead to slap around a welfare deadbeat. Never mind that the G.O.P. is running on empty, with no ideas beyond the incessant repetition of Reagan’s name. A battle over race-and-gender identity politics among the Democrats, with its acrid scent from the 1960s, might be just the spark for a Republican comeback. (As long as the G.O.P.’s own identity politics, over religion, don’t flare up.) Alas, these hopes faded on Tuesday night. First, the debating Democrats declared a truce, however fragile, in...