The 2018 SC-1st Congressional district GOP Primary, a surprise upset for Trump Ally and Staunch conservative Katie Arrington over Veteran Republican incumbent and Former Governor Mark Sanford was a pivotal primary in 2018, one which played a major factor in SC-01 flipping to the Dems that year.
Running close to Trump and as a pollitical outsider, Arrington—a cybersecurity consultant—benefitted from fatigue with the disgrased former governor who back in 2010 had an affair with an Argentinian woman and had several ethics issues because of said affair: with it becoming a national punchline.
This, plus her highlighting anti-Trump stances Stanford took durring the 2016 primary season, and the incumbent sleeping at the wheel—he only spent 500K in the primary, leaving $1.5 Million in his bank account—allowed her to oust the incumbent Republican, becoming the district's GOP nominee.