South Carolina Democratic Primary

After reading CNN’s article, Steady to strong turnout as South Carolina votes, to which CNN's Peter Hamby, Alexander Mooney, Bill Schneider, Suzanne Malveaux and Jessica Yellin contributed, it was discussed that “blacks hold the key to victory” in South Carolina. It also states that Obama will gain legitimate standing with the Democratic Party if he wins the black vote by a solid margin. But here is my question: why is it so crucial for him to have the support of the black community, especially when he won in Iowa where there are virtually only white voters. Shouldn’t the focus be on getting the support of various communities so that you are representative of the country as a whole? Maybe I’m too idealistic, but why just because he is black should he have the support of the black community, and furthermore, why since Hillary is a female should she have the support of the female population in order to validate their run for the White House. Each of these communities is equally crucial to both of the candidates, not just the ones that mirror each candidate’s exterior.