Correction: In a previous edition, the article incorrectly identified Mark Sanford as a Democrat. He is a Republican. This version has been corrected.

Former South Carolina governor Mark Sanford addresses supporters in Charleston on March 19 after advancing to the GOP primary runoff in a race for a vacant congressional seat. Sanford, trying to make a political comeback, was one of 16 Republicans running in Tuesday's primary. (Bruce Smith/AP)

Former governor Mark Sanford took a step closer to returning to elected office Tuesday, advancing to a Republican runoff in South Carolina’s 1st District special election.

With all votes tallied, Sanford led the field of 16 with 37 percent of the vote, a strong showing considering the crowded contest. Former Charleston County Council member Curtis Bostic narrowly won the second spot in the runoff, edging out state Sen. Larry Grooms by fewer than 500 votes, a margin slim enough to trigger a mandatory recount. Grooms strategist Hogan Gidley said late Tuesday that the state senator was not planning to concede to Bostic.

Sanford will face the second-place finisher in an April 2 runoff.

In the Democratic race, Elizabeth Colbert Busch, the sister of Comedy Central host Stephen Colbert, easily captured the nomination over Ben Frasier.

The vacancy was triggered by former congressman Tim Scott’s departure for the Senate. After Jim DeMint (R) abruptly announced his resignation from the Senate, Republican Gov. Nikki Haley appointed Scott (R) to the seat.

Sanford, a onetime rising national GOP star, fell from grace in 2009 after disappearing for nearly a week and admitting to an extramarital affair.

He’s back two years later, trying to reclaim a seat he once held. Sanford represented the district for six years before becoming governor.

Whoever emerges as the GOP nominee will be a heavy favorite in the May 7 election in the heavily Republican district.Nearly six in 10 voters there went with Mitt Romney in the 2012 presidential election.

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