Barack Obama's presidential campaign, until now, has benefited from a strong undercurrent of black nationalism among African-American voters, a racial pride and solidarity that have swelled support and muffled criticism. But his repudiation this week of his longtime pastor, the Rev. Jeremiah Wright Jr., may unleash a more open debate in the black community, where even some who back Obama worry that he is vague or evasive in his approach to race matters. "In some ways it's a cathartic moment for African-Americans whose voices had been silenced," said Andra Gillespie, a political scientist at Emory University. There is no reason...