An anxious murmur is rising among black voters as the presidential race tightens: What if Sen. Barack Obama loses? Black talk-show hosts and black-themed Web sites are being flooded with callers and bloggers reflecting a nervousness—and anger—over the campaign. Monday night, Bev Smith, a nationally syndicated black talk-show host in Pittsburgh, devoted her entire three-hour show to the question: “If Obama doesn’t win, what will you think?” “My audience is upset,” she said. “Some people said they would be so angry it would be reminiscent of the [1960s] riots—that is how despondent they would be.” Warren Ballentine, a nationally syndicated...