Trey Gowdy (committe chairman) was not primaried, but lost favor with Republicans saw the writing on the wall and did not run in 2018.
He faced criticism from Trump supporters for defending the FBI and Special Counsel Robert Mueller's investigation into Russian interference in the 2016 election, which was at odds with Trump's narrative.
Gowdy challenged President Trump's accusation saying that the FBI had spied on his 2016 presidential campaign. As a result Gowdy was attacked by various Trump allies; Politico reported that Gowdy was "virtually alone, getting little support from his House colleagues".