Few senators, past or present, have made their presence felt as often as former Democratic Sen. Carol Moseley-Braun, the first black woman ever elected to the Senate who now wants to become the nation's first black - and female - president. After one term on Capitol Hill, the 55-year-old Moseley-Braun was dethroned amid charges of campaign-finance irregularities and an unsanctioned visit to Africa. (After one door closed for the defeated lawmaker, another soon opened, as President Clinton named her ambassador to New Zealand.) Now the former senator from Illinois has informed the Democratic National Committee that she intends to return...