South Carolina Republicans are locked in a tight matchup in the race to replace the late Sen. Lindsey Graham in the U.S. Senate, with the special primary election set for Tuesday.

Sen. Darline Graham Nordone (R-SC), Graham’s sister who filled the late lawmaker’s unexpired term, was endorsed by President Donald Trump for the Aug. 11 special primary election. Nordone is taking on Rep. Ralph Norman (R-SC), Rep. Russell Fry (R-SC), businessman Mark Lynch, and former Gov. Mark Sanford in the primary to see who will face Democrat Annie Andrews in the November general election.