Former GOP congressman horrified after Mark Sanford loses primary for 'speaking his mind' about Trump
Mark Sanford of South Carolina speaking at the 2013 Liberty Political Action Conference (LPAC) in Chantilly, Virginia. (Gage Skidmore/Flickr)

A former Republican member of the U.S. House of Representatives expressed shock on Wednesday over the defeat of incumbent Republican South Carolina Rep. Mark Sanford.

Pro-Trump candidate Katie Arrington, a state lawmaker, defeated Sanford in the state’s primary on Tuesday.

Sanford had frequently criticized the president, but former GOP congressman Reid Ribble (WI) noted that Sanford had still voted to support most of Trump’s agenda in Congress.

Ribble wrote on Twitter: "[Sanford] supported POTUS with his votes. Pro-tax reform. Repeal Obamacare. Opposed outrageous spending. Yet because he was willing to honor Article 1 Separation of Powers and speak his mind, he loses a primary? We have entered the twilight zone..."

Trump had thrown his support behind Arrington prior to the election.

“My political representatives didn’t want me to get involved in the Mark Sanford primary thinking that Sanford would easily win - but with a few hours left I felt that Katie was such a good candidate, and Sanford was so bad, I had to give it a shot. Congrats to Katie Arrington!” the president tweeted Wednesday morning.