Bob Conley, a pilot and engineer from North Myrtle Beach, appeared to squeak out a narrow win in the U.S. Senate Democratic primary Tuesday.
Conley, 42, held a narrow edge over Michael Cone, a 38-year-old attorney and former naval officer.
But the margin was so small, it falls within state guidelines for an automatic recount.
If the margin holds, Conley would move on to face U.S. Sen. Lindsey Graham.
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Graham, 52, an attorney and a member of the Senate since 2003, decisively defeated dentist Buddy Witherspoon, 69.
Graham has angered some conservative Republicans by striking a deal with Democrats to prevent them from filibustering President Bush's judicial appointments.
But Graham's policies potentially make him more appealing to moderates and more difficult to defeat.
Looking toward November, Graham has backed Bush's approach to the war in Iraq, while Conley believes U.S. troops should be withdrawn.
Conley also has called for the U.S. to pull out of trade agreements he argues have led to a loss of American jobs and for the passage of a new “G.I. Bill of Rights” to aid veterans.