(CNN) President Donald Trump's decision Tuesday to go after an incumbent Republican congressman who had previously criticized him flouted the advice of allies who suggested he stay out of the race.

Rep. Mark Sanford, a rare conservative member who was also critical of the President, lost his GOP primary on Tuesday to Katie Arrington, a South Carolina state representative who made Sanford's negative comments about Trump the focus of her campaign.

Just hours before the polls closed in Sanford's district, Trump slammed the former South Carolina governor on Twitter and endorsed Arrington -- much to the dismay of the House Freedom Caucus, of which Sanford is a member. In a rare dissent from the President, Rep. Mark Meadows issued a statement shortly after Trump's tweet that reaffirmed he was "very supportive" of Sanford's re-election bid.

One White House aide said Trump's disdain for Sanford should not have come as a surprise to the conservatives now protesting the President's intervention in his primary.

"Sanford is the worst and has been against the President and our policies from Day One," the aide said. "It should be no surprise to the Freedom Caucus that the President came out against him in the primary."

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