Voters in five states head to the polls Tuesday, with most of the action in House primaries.

Republican Rep. Mark Sanford is facing a party challenge for his South Carolina seat. Nominees will be chosen in a half-dozen other competitive House races. And a new voting process will be tested in Maine.

Here’s what to watch in each of the states:

South Carolina

A threat from Sanford’s right flank has been brewing for much of the past year in the safe Republican 1st District, but it’s only recently that the congressman has responded, spending money on TV ads for the first time in five years, according to Politico.State Rep. Katie Arrington has tried to make her professed loyalty to President Donald Trump a big part of her primary campaign against Sanford, who’s been outspoken against the president and sometimes his own party, including on issues such as climate change, important to the Charleston-area district. (Asked about anthropogenic climate change in an interview with Roll Call last year, Arrington said: “Climate change is something that has happened naturally, that’s why we are not living on ice anymore. It will go around and come around.”)Watch: What You Need to Know for Tuesday’s Primaries in 5 States

Arrington has also hinted at Sanford’s controversial past as governor, not-so-subtly alluding to his 2009 disappearance when his office claimed he was hiking the Appalachian Trail but he was actually seeing his Argentinian mistress. “Bless his heart,” she says in a recent TV spot filmed on a woodsy trail. “But it’s time for Mark Sanford to take a hike — for real this time.”

Arrington has kicked nearly $430,000 of her own money into her campaign. She ended the pre-primary reporting period with $199,000 to Sanford’s $1.6 million. Despite trying to run to his right, Arrington told Roll Call last year she wouldn’t join the Freedom Caucus, of which Sanford is a member. FreedomWorks and Tea Party Patriots are standing with the incumbent.

Elsewhere in the Palmetto State, 13 Republicans are vying for the open 4th District seat that House Oversight Chairman Trey Gowdy is vacating. Inside Elections with Nathan L. Gonzales rates the race Solid Republican, so whoever wins is likely coming to Congress next year. In a sign of just how conservative the district is, all of the candidates disavowed the pro-business U.S. Chamber of Commerce at a tea party forum earlier this year. The anti-tax Club for Growth has backed former Spartanburg County GOP chairman Josh Kimbrell. The National Association of Realtors is supporting state Rep. Dan Hamilton. If no one wins a majority, the top-two finishers will advance to a June 26 runoff.

Maine

Three Democrats are competing to take on GOP Rep. Bruce Poliquin in Maine’s 2nd District, which will use ranked-choice voting for the first time. Under the system, voters will rank each candidate on the ballot and if no one wins a majority of first-place votes, votes from the third-place finisher will be reapportioned to the other two candidates depending on those voters’ second-choice preferences. The primary is a close race between state House Assistant Majority Leader Jared Golden, a Marine veteran, and conservationist Lucas St. Clair, who’s benefiting from late outside spending. Inside Elections rates the general election Leans Republican. (Read much more about the primary here.)

Virginia

The biggest primary to watch in the Old Dominion is in the competitive 10th District that Hillary Clinton carried by 10 points in 2016. Six Democrats are vying to take on two-term GOP incumbent Barbara Comstock. All eyes are on state Sen. Jennifer Wexton, who already represents a good portion of the district. She’s the only elected official running in the primary and has the support Gov. Ralph S. Northam and local elected officials, and The Washington Post’s endorsement.

Three other Democratic women are running. Former State Department official and anti-human trafficking activist Alison Friedman had loaned her campaign more than $1 million by end of the pre-primary reporting period. She has outspent the other contenders, and is also benefiting from a super PAC called Defeat Slavery. Friedman was the first candidate to go on the air, running an ad about gun control — a popular issue for Democrats in this primary.

Former Obama administration official Lindsey Davis Stover, who was chief of staff to former Texas Rep. Chet Edwards, has also raised significant resources. She has talked about being raised by a single mother and working her way through college, a message her campaign hopes will resonate in less affluent pockets of the district. The Pride Fund to End Gun Violence has endorsed her.

Army veteran Dan Helmer has raised over $1 million and attracted earned media attention for his offbeat ads, including a recent spot that compared Trump to Osama bin Laden and provoked a response from the White House. He has the backing of VoteVets, which made a small TV buy for him.

Former Justice Department official Paul Pelletier and scientist Julia Biggins are also running but both have raised and spent less money than the others.

On the Republican side, Comstock does have a primary challenger, but retired Air Force pilot Shak Hill had raised only $245,000 to her $3.2 million by the end of May. Still, Comstock isn’t taking the threat lightly. She spent $596,000 during the pre-primary period (more than she raised) and her campaign set up a website and has run radio ads against Hill. Vice President Mike Pence recorded a phone message for Comstock, according to The Washington Post.  

The 10th District general election is rated a Toss-up.

Elsewhere in Virginia, voters in the 7th District will pick a Democrat to take on GOP Rep. Dave Brat, whom some Republicans worry isn’t taking his re-election seriously enough. Both retired CIA officer Abigail Spanberger and Marine veteran Dan Ward are running on their records of service and have raised significant money. Spanberger has tapped into the grass-roots energy that mobilized the area during the 2017 state elections and has the backing of EMILY’s List. VoteVets and organized labor are backing Helmer. Inside Elections rates the general election Leans Republican.

The GOP Senate primary to take on Democratic incumbent Tim Kaine has received less attention since the race is rated Solid Democratic. Corey Stewart, the chairman of the Prince William County Board of Supervisors, narrowly lost the GOP gubernatorial nomination last year and is running a similarly controversial campaign again. Americans for Prosperity has endorsed state Del. Nick Freitas, a retired Green Beret who has called out Stewart for standing with white supremacists. Also running is evangelical pastor E.W. Jackson, the losing GOP nominee for lieutenant governor in 2013, but he has raised less money.

Nevada

The Senate primary drama in Nevada dissipated once Danny Tarkanian dropped his challenge to GOP Sen. Dean Heller and opted to instead run again for the 3rd District, which Democratic Rep. Jacky Rosen in turn is vacating for a Senate bid. She is expected to secure the party nod to take on Heller, despite having a self-funding primary opponent.

While Tarkanian lost to Rosen in the 3rd District in 2016, some operatives watching the race expect him to emerge from the crowded GOP primary field for the open seat, given his high name ID as a frequent candidate. He also brought a sizable war chest from his Senate race to the House contest, ending the pre-primary reporting period with $702,000 on hand. Other GOP candidates in the mix include state Sen. Scott Hammond, who has been endorsed by the National Rifle Association, and former television news reporter Michelle Mortensen.

Philanthropist Susie Lee is expected to win the Democratic nomination. The education advocate, she has raised nearly $1.5 million so far, ending the pre-primary period with $856,000 in her campaign coffers. She has been endorsed by former Vice President Joseph R. Biden, Jr., and was added to the Democratic Congressional Campaign Committee’s Red to Blue program for strong challengers. Trump carried the district by 1 point in 2016. Inside Elections rates the race Tilts Democratic.

The DCCC has also weighed in on Nevada’s open 4th District contest, effectively backing former Democratic Rep. Steven Horsford by adding him to Red to Blue. Horsford is considered the front-runner among six Democrats competing for the seat vacated by Democratic Rep. Ruben Kihuen, who is retiring following allegations of sexual harassment. Others in the primary include state Sen. Pat Spearman; high school principal John Anzalone; businesswoman Amy Vilela; and Allison Stephens, a member of the Nevada System of Higher Education Board of Regents.

Former GOP Rep. Cresent Hardy is expected to win the GOP nomination in and could potentially face a rematch with Horsford, whom he defeated in 2014. It would be one of the more unusual matchups of the cycle, pitting two former members against one another. Republicans are targeting the expansive 4th District that stretches north of Las Vegas, although Democrats are confident of holding on to the seat that Clinton carried by 5 points in 2016. Inside Elections rates the general election Likely Democratic.

North Dakota 

GOP Rep. Kevin Cramer’s decision to run for Senate opened up his at-large seat, where the winner of the Republican primary will be in a strong position to win in November. State Sen. Kelly Armstrong has the state GOP’s endorsement. (He previously served as the state party chairman but stepped down when he announced his campaign in February.) Fellow Republican state Sen. Tom Campbell dropped out of the race in April and backed Armstrong. Two other GOP candidates are running: Iraq War veteran Tiffany Abentroth and Paul Schaffner, who was arrested last year during a prostitution sting.North Dakota Democrats endorsed former state Senate Minority Leader Mac Schneider at the party convention in March. Schneider faces an uphill climb in a state that Trump carried by 36 points in 2016. Inside Elections rates the general election Solid Republican.