Backed overwhelmingly by African American voters, former Vice President Joe Biden sweeping victory in South Carolina’s Democratic presidential primary on Saturday has made him the leading alternative to frontrunner Sen. Bernie Sanders on Super Tuesday and put fresh pressure on other contenders to drop out. It is just as Biden’s campaign promised after a disappointing fourth-place finish in Iowa and an even worse fifth place in New Hampshire: When the election moved to more diverse states, Biden started to fare better, starting with a second-place finish in Nevada, and now a decisive win in South Carolina . Biden’s triumph in South Carolina, years in the making, was the first time he has won a contest outside his home state of Delaware in his three runs for the Democrats’ presidential nomination . It was a show of grit and grind, made possible in no small measure by the endorsement of the state’s longtime kingmaker, Rep. James Clyburn, earlier in the week. More than half o...