2018 Election: Primary results in Nevada, Virginia, Maine, North Dakota and South Carolina

On Tuesday, five states – Nevada, Maine, North Dakota, South Carolina and Virginia – voted to determine party nominees ahead of November's midterm elections.

Here are some key takeaways from Tuesday's primaries:

• Rep. Mark Sanford (R., S.C.) conceded in his primary against fellow Republican Katie Arrington, which pitted a critic of President Trump against an outspoken supporter.

• Democrats face a difficult Senate map in 2018, which means defending seats in states won overwhelmingly by President Trump in 2018. One is the seat held by Sen. Heidi Heitkamp (D., N.D.), whom Trump can't stop saying nice things about.

• In Wisconsin, Democrats claimed victory in a special election for a Republican-held state Senate seat. It is the 43rd legislative seat Democrats have flipped from Republican control since President Trump took office.

Here are results from the already-held primaries in Pennsylvania and New Jersey, and a brief run-down of what happened Tuesday night.

While none of South Carolina's House seats are expected to be competitive in November, incumbent Rep. Mark Sanford conceded in the Republican primary for his First Congressional District seat against state Rep. Katie Arrington. Arrington had attacked Sanford from the right, painting him as disloyal to Trump, and the president himself slammed Sanford as "unhelpful" and "nothing but trouble" on Twitter just hours before the polls closed.

"He is better off in Argentina," Trump wrote, alluding to a highly publicized extramarital affair Sanford had while serving at the state's governor.

Sanford has been one of Trump's most outspoken Republican critics. Sanford said Trump's travel ban on Muslim-majority countries "fanned the flames of intolerance" and claimed that to the president, "facts don't matter." Despite his vocal opposition, Sanford has voted with Trump over 73 percent of the time, according to FiveThirtyEight.

"If Sanford falls tonight, will this become the new normal?" CNN White House correspondent Jeff Zeleny wrote on Twitter. "This South Carolina primary will test how big the GOP tent still is and whether there's any room for dissent."

Sanford is the second Republican congressman ousted in a primary this year. Rep. Robert Pittenger (R., N.C.) was defeated by conservative pastor Mark Harris in a race last month.

Nevada's Senate primary became much less interesting when businessman Danny Tarkanian was persuaded by Trump to end his challenge to Republican incumbent Sen. Dean Heller. in November, Heller will face Rep. Jacy Rosen, who easily won the Democratic nomination in a six-person primary.

Rosen is vacating her seat in the Third Congressional District, where philanthropist Susie Lee easily won the Democratic nomination Tuesday night. On the Republican side, Tarkanian (who is now running for the House instead of the Senate) won his primary fight against state Sen. Scott Hammond and former reporter Michelle Mortensen.

The Fourth Congressional District is also expected to be competitive come November. Former Rep. Cresent Hardy took home the Republican nomination, while former Rep. Steven Horsford won the Democratic nomination after incumbent Ruben Kihuen announced he wouldn't seek reelection in response to sexual misconduct allegations.

Virginia features four House races that are expected to be competitive in November's general election. Three had primary elections Tuesday night.

In the Second Congressional District, incumbent Republican Rep. Scott Taylor will face off against former U.S. Navy commander Elaine Luria in November. Luria, who was backed by the Democratic Congressional Campaign Committee, earned the Democratic nomination by defeating schoolteacher and first-time candidate Karen Mallard.

In the Seventh Congressional District, incumbent Republican Rep. Dave Brat will face off against former CIA operative Abigail Spanberger, who easily defeated retired Col. Dan Ward in the Democratic primary. Cook Political Report calls the seat a "toss up."

In the 10th Congressional District, incumbent Rep. Barbara Comstock is widely viewed as one of the nation's most-vulnerable Republicans. Comstock will be challenged in November by state Sen. Jennifer Wexton, who defeated former Obama administration staffers Alison Kiehl and Lindsey Davis Stover and veteran Dan Helmer to earn the Democratic nomination.

Sen. Tim Kaine is among the Democrats forced to defend their seats in November, though the party's former VP candidate isn't expected to face much of a contest. Kaine's general election opponent will be Republican Corey Stewart, a one-time state chairman of President Donald Trump's 2016 presidential campaign who focused his failed campaign for governor last year on preserving Virginia's Confederate monuments.

The big race in Maine in November will be for governor, where Democrats see an opportunity to flip a Republican seat held by outgoing Gov. Paul LePage. State Attorney General Janet Mills is expected to win the Democratic nomination, while business executive Shawn Moody was the frontrunner in a close, four-person race for the Republican nomination. As of Wednesday morning, the Republican primary was too close to call.

Almost as big as the election itself is how voters are making their choices. Instead of picking their preferred gubernatorial candidates, voters will instead rank their choices from first to last – a system many have compared to an instant primary runoff. As the Washington Post's Amber Phillips points out, advocates say it forces candidates to reach out to a broader group of voters.

The Second Congressional District is also expected to be competitive in November. Republican incumbent Rep. Bruce Poliquin will attempt to defend his seat against the winner of a three-person Democratic primary featuring state Rep. Jared Golden, bookseller Craig Olson and nonprofit director Lucas St. Clair. Golden was ahead by about 3,000 votes Wednesday morning, but this race remains too close to call.

If Democrats have any shot of winning control of the Senate, they'll need to successfully defend Sen. Heidi Heitkamp's seat in a state President Trump won by more than 30 points in 2016. Rep. Kevin Cramer easily won the Republican nomination Tuesday night, but he's still upset that Trump, who Cramer claims "begged" him to give up a safe seat in Congress to run against Heitkamp, can't stop praising his Democratic opponent.

"I do think there's a little difference in that she's a woman," Cramer told the Washington Post. "That's probably part of it — that she's a, you know, a female. He doesn't want to be that aggressive, maybe. I don't know."