The South Carolina race highlighted primary voting in five states on Tuesday.
Sanford told his supporters shortly before 11 p.m. he was likely to lose his bid for re-election Tuesday night. Last week Alabama GOP Rep. Martha Roby was forced into a runoff election after a primary contest that centered on her decision not to vote for President Trump following the October 2016 publication of his vulgar comments during a filming of "Access Hollywood".
"It's time for a conservative who will work with President Trump, not against him", Arrington said in her closing TV spot attacking Sanford. Trump didn't even endorse his opponent until the polls were nearly closed last night.
Sanford is a former governor who has never lost an election in eight races in SC, even after he admitted to an affair with a woman in Argentina.
In conceding the race, Sanford said he was comfortable with the positions he took on Trump.
"He is MIA and nothing but trouble", Trump tweeted.
"If Mark had gotten behind the president, the Affordable Care Act would be where it is today", Arrington told McClatchy in January.
He tweeted again Wednesday mornings, saying that his political representatives thought Sanford would "easily win".
With 16 percent of the vote in for South Carolina's 1st District, both incumbent Mark Sanford and challenger Katie Arrington remain almost tied, with the AP giving both candidates 48 percent. But in the South Carolina GOP primary race for governor, the president's backing was not enough; that race is headed to a runoff in two weeks. Smith won the Democratic nomination on Tuesday after leading the pack in fundraising, endorsements and name recognition.
In the Seventh Congressional District, incumbent Republican Rep. Dave Brat will face off against the victor of a Democratic primary between former Central Intelligence Agency operative Abigail Spanberger and retired Col. Dan Ward.
Sanford is a second U.S. House member from the South attacked by a challenger for criticizing Trump.
The race is perhaps the most closely watched matchup in Tuesday's slate of primaries, which also include Virginia selecting a Republican to take on Democratic Sen. Voters will settle about 30 primary battles for state legislative seats. Heidi Heitkamp of North Dakota.
To date, 476 women have filed to run for the House in 2018, according to the Center for American Women and Politics at Rutgers University, surpassing the 272 who filed in 2016. She will face another another woman, State Sen.
Democrats will also be watching the outcomes of Virginia's 2nd District (GOP Rep. Scott Taylor), 7th District (GOP Rep. Dave Brat) and 5th District (retiring GOP Rep. Tom Garrett), where they hope to be competitive in the fall.
Inside Elections with Nathan L. Gonzales rates the general election Solid Republican.
Republican candidates included: Shannon Pierce, Claude Schmid, Lee Bright, John Marshall Mosser, Mark Burns, Dan Albert, Barry Bell, Stephen H. Brown, William Timmons, Dan Hamilton, Justin David Sanders, Josh Kimbrell and James Epley.