- President Donald Trump endorses Katie Arrington, who is challenging Rep. Mark Sanford in Tuesday's South Carolina 1st District primary.
- Trump contends Sanford has been "unhelpful" to his agenda.
- The president also references the congressman's extramarital affair, saying Sanford is "better off in Argentina."
President Donald Trump highlighted Republican Rep. Mark Sanford's extramarital affair Tuesday as he boosted the South Carolina congressman's challenger.
In a tweet sent only a couple hours before primary election polls close in the state, the president endorsed Sanford's opponent, Katie Arrington. Seizing on Arrington's attack line in the race, Trump contended the congressman "has been very unhelpful" to his agenda and "nothing but trouble."
"He is better off in Argentina," the president added. The sentence alludes to the former South Carolina governor's disappearance in 2009. While he claimed to be hiking the Appalachian Trail, he was really in the South American country visiting a woman with whom he was having an affair.
A president campaigning against a sitting member of Congress from his own party is rare. Sanford's campaign did not immediately respond to a request to comment.
It is unclear how much of an effect Trump's endorsement could have on the South Carolina 1st District GOP primary, as polls close at 7 p.m. ET. The GOP primary winner in the Republican-leaning district will be favored in November's general election.
Allegiance to Trump has played an important role in both House and Senate primaries in red pockets of the country. State Rep. Katie Arrington has made supporting the president a centerpiece of her campaign.
"It's time to turn the page on the Mark Sanford era. It's time for a new Republican voice in Congress. It's time for a conservative who will work with President Trump, not against him," she said in a recent television ad.
In another ad, she tells voters: "It's time for Mark Sanford to take a hike — for real this time."
Sanford has served in Congress since 2013. He has taken a libertarian lean, preaching fiscal conservatism. He broke with Trump to vote against the $1.3 trillion spending bill passed earlier this year. The legislation included massive funding increases for both defense and domestic programs.
He also recently opposed the farm bill backed by Trump and other GOP leaders.
Sanford also may have earned Trump's ire for his comments about the president's effect on political discourse. Following the shooting of House Majority Whip Steve Scalise last year, Sanford said Trump is "partially to blame for demons that have been unleashed."
In a tweet responding to Trump's endorsement of Arrington, Republican Rep. Justin Amash said Sanford is "one of the most principled, consistent, and conservative members of Congress I've ever known."
"And unlike you, Mark has shown humility in his role and a desire to be a better man than he was the day before," the Michigan congressman added.