If you've paid attention to Democratic presidential politics in recent decades, you know South Carolina matters – an early test in the primary race, and a true center of power in the Democratic Party. Though African-Americans are a quarter of South Carolina's population, Jim Clyburn is the state's sole Black representative (and Democrat) in the U.S. House. And over 33 years, Clyburn – a civil rights activist, party strategist, and political kingmaker – has built his political network one