Mark Sanford, Stephen Colbert's Sister, Among Candidates in Today's Primaries for Vacant House Seat

Tim Scott's departure for the Senate left a vacancy; primary run-off in April, special election in May

Disgraced ex-governor Mark Sanford faces the first test of his political comeback bid on Tuesday, as South Carolina voters choose their nominees for a vacant congressional seat.

Sanford is expected to be the top vote-getter among 16 Republicans running to replace Tim Scott in the U.S. House. The open question is who will face Sanford, whose extramarital affair in 2009 derailed his political career, in an April 2 runoff.