In recent decades, South Carolina has become the Democratic Party's make-or-break proving ground for White House hopefuls - and Congressman Jim Clyburn, the state's sole Black Democrat in the U.S. House of Representatives, is one of the party's most important voices. The civil rights veteran talks with "Sunday Morning" national correspondent Robert Costa about his decision to seek re-election for an 18th term; fighting efforts to roll back voter protections established by the 1965 Voting Rights Act; and how President Trump might react if Democrats win back the majority in Congress.