Darline Graham has won South Carolina's Republican Senate primary runoff, defeating Congressman Ralph Norman despite a series of embarrassing debate gaffes, largely thanks to strong backing from President Donald Trump. Graham, the adopted sister of the late Senator Lindsey Graham, entered the race at Trump's encouragement after her brother's death, and his endorsement proved decisive in overcoming doubts among South Carolina Republicans about her limited public service experience.

Trump campaigned heavily for Graham in the race's final days, holding rallies in Myrtle Beach and tele-rallies urging supporters to vote as if he himself were on the ballot, while the pro-Trump super PAC MAGA Inc. spent over $827,000 backing her. This support helped her win decisively in Horry County, offsetting a damaging debate performance in which she admitted she was "not that informed on national security" and wrongly claimed 50 million people in South Carolina lived paycheck to paycheck, despite the state's population being roughly 5.5 million. Norman, who campaigned on his foreign policy experience, won north-western counties around Greenville but could not close the gap. Graham now heads into the general election as the strong favourite against Democrat Annie Andrews, a paediatrician.