WASHINGTON (CNN) - Polls are closed in South Carolina, Virginia and Maine as voters there choose candidates in key primaries ahead of November's midterm elections.
Polls will close at 10 p.m. EDT in Nevada. All polls in North Dakota will be closed by 9 p.m. EDT.
Hours before the first polls closed, President Donald Trump tweeted out his picks in two primary races.
Trump urged South Carolina voters to pick Republican candidate Katie Arrington over incumbent Rep. Mark Sanford, whom Trump attacked in a tweet by invoking the congressman's 2009 extra-marital affair.
"Mark Sanford has been very unhelpful to me in my campaign to MAGA," Trump tweeted. "He is MIA and nothing but trouble. He is better off in Argentina. I fully endorse Katie Arrington for Congress in SC, a state I love. She is tough on crime and will continue our fight to lower taxes. VOTE Katie!"
The race between Sanford and Arrington provides the latest test of just how willing Republican voters are to stomach congressional criticism of 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. Tim Kaine and choosing nominees in several competitive House races, Nevada and North Dakota choosing their Senate candidates and Maine for the first time trying -- and voting on whether to keep -- a new voting system in which voters rank their preferences, rather than only selecting one.
Trump also tweeted his endorsement of Adam Laxalt, Nevada's attorney general, just after noon Pacific time. "I strongly endorse Adam Laxalt for Governor of Nevada," he tweeted. "Adam is smart, works hard, and knows how to win. He will be a great Governor. Also, will fight hard to lower your taxes and is tough on crime!"
Tuesday's House races
Sanford's seat is likely to remain in Republican hands no matter the winner of Tuesday's primary.
But in Virginia, Democrats are selecting House candidates to run in some of the nation's most competitive races.
Republican Rep. Barbara Comstock in northern Virginia's 10th District will face the winner of a six-way Democratic primary. State Sen. Jennifer Wexton is the establishment preference, but veteran Dan Helmer's viral ads -- one of which compares the threat Trump poses to Osama bin Laden -- have gained some national attention.
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.
Another House race worth watching is in South Carolina, where Archie Parnell is poised to win the Democratic primary in the 5th District despite admitting to domestic abuse in the 1970s. Local, state and national Democrats have called on him to drop out of the race in the deep-red district and say they won't support him if he wins.
In Nevada, the parties will choose their nominees in two competitive open seats. In the 4th District, vacated by retiring Rep. Ruben Kihuen, two former congressmen -- Democrat Steven Horsford and Republican Cresent Hardy -- are the favorites. ...