- Primary elections will take place Tuesday in Ohio, Indiana, West Virginia and North Carolina.
- Voters will choose challengers to vulnerable Democratic Sens. Joe Manchin and Joe Donnelly in West Virginia and Indiana, respectively.
- Parties will set their nominees for multiple competitive House races in Ohio and North Carolina.
- In Ohio, both Republican and Democratic primaries for governor are competitive.
A string of 2018 primary elections take place Tuesday, shaping elections that will help to determine which party holds the House and Senate after November's midterms.
Indiana, North Carolina, Ohio and West Virginia will hold primaries Tuesday. Both West Virginia and Indiana will hold critical Senate elections, while intriguing House and governor races will play out in Ohio and North Carolina.
West Virginia and Indiana have become top battlegrounds in the fight for the Senate, which Republicans currently control. Meanwhile, House races in both Ohio and North Carolina will factor into whether Democrats can win enough seats to take control of the chamber.
Here are some of the races to watch Tuesday:
West Virginia voters will select a Republican nominee to challenge Democratic Sen. Joe Manchin, one of the most vulnerable senators running for re-election this year. Trump won the state by about 40 percentage points in 2016, making it a prime pickup opportunity for Republicans.
The party sees trouble in one potential outcome. Republicans fear former coal executive Don Blankenship will struggle to defeat Manchin in November. The ex-Massey Energy CEO served jail time for his role in a mine explosion that killed 29 people.
He also has earned the ire of Republican leaders with racially charged attacks on Senate Majority Leader Mitch McConnell and Transportation Secretary Elaine Chao, the Kentucky Republican's wife. The GOP prefers either Rep. Evan Jenkins or West Virginia Attorney General Patrick Morrisey.
On Monday, President Donald Trump urged West Virginia voters not to support Blankenship, arguing that he cannot beat Manchin. In his tweet, Trump did not criticize Blankenship's character or ads, but focused on the political implications of him winning the primary.
Public polling has been scarce: one Fox News poll last month found Jenkins garnering 25 percent support, followed by Morrisey and Blankenship with 21 percent and 16 percent, respectively. A Weekly Standard report says internal polls found Blankenship winning more support and taking a narrow lead ahead of Tuesday's primary.
In Indiana, Republicans are fighting for the chance to take on Democratic Sen. Joe Donnelly, another one of the chamber's most endangered members. Trump won the state by about 20 percentage points, buoying the GOP's hopes that it can flip Donnelly's seat.
Since Trump has strong support in the state, Republicans running in the primary have tried to emulate the president. Reps. Todd Rokita and Luke Messer, and Mike Braun, a businessman and former state representative, have all tried to channel Trump in their own ways.
The only public poll taken in the race last month found a 10-point advantage for Braun. However, nearly half of those surveyed were undecided, suggesting no clear front-runner with only days to go.
Like Manchin and Donnelly, Sen. Sherrod Brown is among the 10 Democrats running this year in states Trump won in 2016. The Ohio Democrat, up for re-election in a purple state that Trump carried by about 8 points, appears safer this year than his colleagues in West Virginia and Indiana.
On the Republican side, Trump-backed Rep. Jim Renacci appears to have the advantage in the race to take on Brown. He faces businessman Mike Gibbons in Tuesday's GOP primary.
Brown, who has preached populist policies that sometimes align with Trump, has held the seat since 2006.
In Ohio and North Carolina, voters will choose nominees for a few seats that have a chance to be competitive in November. In Indiana and West Virginia, the primaries will determine candidates for seats largely considered safe for one party.
- Ohio will hold a primary for the state's 12th District, which was vacated by GOP Rep. Pat Tiberi's resignation. Tuesday's winners will face off in a special election in August to fill the remainder of Tiberi's term. The seat is typically considered safe for Republicans, but recent Democratic improvement in multiple special elections signals it could become more competitive than usual.
- Democrats will determine challengers to GOP congressmen in other Ohio districts that could prove important later this year. The party will choose challengers to Rep. Steve Chabot in the 1st District, Rep. Mike Turner in the 10th District, Rep. Dave Joyce in the 14th District and Rep. Steve Stivers in the 15th District.
- In North Carolina's 9th District, GOP Rep. Robert Pittenger faces both a Republican primary challenger and a well-funded potential Democratic opponent. The state's 13th District, represented by Republican Ted Budd, could also be in play this year.
- Rokita and Messer in Indiana, as well as Jenkins in West Virginia, vacated safe Republican districts to run for Senate. The winner of the GOP primary for those seats — Indiana's 4th and 6th Districts and West Virginia's 3rd District — will likely go on to win the general election. Vice President Mike Pence's brother, Greg, is considered the front-runner to succeed Messer in Indiana's 6th District.
A bitter primary process has played out in the race to succeed Ohio Gov. John Kasich.
On the Democratic side, former Ohio Attorney General and Consumer Financial Protection Bureau Director Richard Cordray is competing against former congressman and presidential candidate Dennis Kucinich, who has billed himself as more progressive than Cordray. Kucinich is also a former mayor of Cleveland.
A major policy fight has played out on gun control. Cordray has tried to appeal to the swing state with a more centrist position on firearms regulation, while Kucinich has proudly flaunted an "F" rating from the National Rifle Association.
In the Republican primary, Ohio Attorney General Mike DeWine and Lt. Gov. Mary Taylor are fighting for the nomination. While both candidates aligned with centrist Trump critic Kasich in the past, they have touted their pro-Trump and conservative credentials during the primary.