The voting in Ohio, Indiana, North Carolina and West Virginia come as Democrats try to wrest control of the U.S. House of Representatives while Republicans try to hold onto their majority and potentially pick up Senate seats.

Here are some races to watch:

West Virginia:

West Virginia’s Senate primary may be the most closely watched of the May 8 primaries, and that’s because of former Massey Energy CEO Don Blankenship. After an explosion at Massey’s Upper Big Branch Mine in 2010 killed 29 miners, he spent a year in federal prison after a federal jury convicted him of conspiring to violate mine safety and health standards.

Blankenship is running against more conventional Republican candidates Rep. Evan Jenkins and Attorney General Patrick Morrisey, while railing against Senate Majority Leader Mitch McConnell (Blankenship calls him “Cocaine Mitch”). Mainstream Republicans worry that Blankenship may score an upset win in the primary, but then, because of his pugnacious style and checkered history, lose the general election in November to incumbent Sen. Joe Manchin II, a moderate Democrat. (Manchin does have a primary challenger, Paula Jean Swearengin, but he is expected to prevail.)

On Monday morning, President Donald Trump tweeted to ask West Virginia voters to steer clear of Blankenship and instead vote for his opponents, saying Blankenship “can’t win the General Election in your State…No way!” Trump also said “Remember Alabama,” invoking Roy Moore’s primary victory in Alabama and eventual loss in the general election after multiple women accused him of sexual misconduct.

To the great people of West Virginia we have, together, a really great chance to keep making a big difference. Problem is, Don Blankenship, currently running for Senate, can’t win the General Election in your State…No way! Remember Alabama. Vote Rep. Jenkins or A.G. Morrisey!

— Donald J. Trump (@realDonaldTrump) May 7, 2018

Ohio:

The House primary races to watch, according to Vox, are in the 1st, 7th, 10th, 12th, 14th, and 15th Congressional districts that Democrats are trying to flip from Republican control.

But the big races to watch are the U.S. Senate and the gubernatorial primaries.

Democratic incumbent Sen. Sherrod Brown is up for reelection, and the May 8 primary will decide who the progressive Senator will face. There are two Republicans in the field: Rep. Jim Renacci—who Trump endorsed—versus businessman Mike Gibbons.

The primary will decide who will fight to replace current Gov. John Kasich, who has can’t run again after serving two terms. The Cincinnati Enquirer has characterized the race as a “wacky, bitter battle.”

On the Republican side, State Attorney General Mike DeWine is up against Lt Gov. Mary Taylor. On the Democratic side, the fight is between former Rep. Dennis Kucinich, and former head of the Consumer Financial Protection Bureau during the Obama administration Rich Cordray.

Indiana:

Indiana is Vice President Mike Pence’s home state, which Trump won by 19 points in the 2016 general election. Eyeing his margin, the three Republican Senate candidates have clung close to Trump as they try to take out Democratic incumbent Sen. Joe Donnelly. They are Rep. Todd Rokita, Rep Luke Messer, and businessman and former Indiana State Rep. Mike Braun. This primary race has been called the “nation’s nastiest,” according to the Indianapolis Star, and it’s unclear who will win.

North Carolina:

Every 12 years, North Carolina has a Blue Moon election—or an election with no statewide races on the ballot—that translates into lower voter turnout. And 2018 is one of them. The primaries to watch, according to The Hill and Vox, are those deciding the Democratic challengers to incumbent Republican Reps. Richard Hudson, Robert Pittenger, Ted Budd, and George Holding.