Hillary Clinton's advisers have a growing fear: that Barack Obama's solid showing in the New Hampshire primary last week and his earlier victory in Iowa have increased confidence among black voters that he can really win the nomination. That might cause thousands of African-Americans to shift from Clinton to Obama in South Carolina, which holds its Democratic primary January 26. One of the biggest obstacles to African-American support for the Illinois senator has been doubt that he could actually defeat Clinton. Now that he has won Iowa, where the electorate is overwhelmingly white, and finished a close second in New Hampshire, which is also dominated by white voters, the doubt is eroding, say senior Democrats in South Carolina. African-Americans constitute a majority of the Palmetto State's Democratic electorate.