With 98-percent of precincts reporting, Arrington led the race by about 2,500 votes - enough to avoid a runoff and secure the Republican nomination.
"I am extremely disappointed that a candidate like Corey Stewart could win the Republican nomination for US Senate", former Virginia Republican Lt. Gov. Bill Bolling tweeted.
Arrington made Sanford's disagreements with Trump a cornerstone of her campaign. The onetime insurgent has made allegiance to his leadership a litmus test in many Republican races.
That was a reference to Sanford's surprise disappearance from the state as governor, which he later revealed was to continue his affair with an Argentine woman.
Congressman Mark Sanford is best remembered nationally for a highly public extramarital affair with a woman in Argentina several years ago.
Trump, who issued his tweet as he returned from his summit with North Korean leader Kim Jong Un, said Sanford "is better off in Argentina".
A record number of Democratic women have filed to run for Congress since President Donald Trump stepped into the White House, with many telling CNN that they chose to run in response to Trump's presidency.More news: Terms agreed for Anthony Joshua unification fight
There are three candidates, including Sanford, in the Republican primary. Mark Sanford, who has held the seat since 2013, trails with 46 percent of the vote. The Congressman's prediction came true, with him conceding to Arrington.
"He's one of the most principled, consistent and conservative members of Congress I've ever known", tweeted Amash, one of the House's most outspoken conservatives. It's Democrats' third big special election win in Wisconsin this year alone, and their 43rd state legislative seat they've flipped in the Trump era.
That includes one of the most competitive districts in the nation, Rep. Barbara Comstock's in the outer D.C. suburbs.
Sanford was critical of Trump during the 2016 presidential campaign, and has found himself on opposite sides with the president since.
If she holds on, Arrington would face Democrat Joe Cunningham in November. Dean Heller. And in North Dakota, Republicans will pick Rep. Kevin Cramer to challenge Democratic Sen.
'Great night for Republicans!' tweeted Trump.
In Nevada, Democrats are set to nominate Rep. Jacky Rosen to take on Republican Sen.More news: Trump, Trudeau trade fight: Map of Canada exports to US
Democrat Abigail Spanberger, a former Central Intelligence Agency operative, won her primary in Virginia's 7th Congressional District to face incumbent Rep. David Brat in the fall.
It was the 58-year-old's first election loss.
Democrats need to gain 23 seats to win the majority in the House.
ME voters are deciding how they'd prefer to veer in their search for the successor to term-limited, conservative Republican Gov. Paul LePage.
There were exceptions in Cherokee and Darlington counties, where sharply contested local races had somewhat heavier turnout, Chris Whitmire with the election commission said.
Maine Secretary of State Matt Dunlap said the election results would be binding anyway, the Portland Press Herald said.More news: Trump’s Trade Adviser Apologizes for ‘Inappropriate’ Trudeau Comments
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