WASHINGTON (AP) — Topping the list of contests in Tuesday’s primaries in four states is a U.S. Senate race in Maryland that has further complicated Democratic efforts to keep control of the narrowly divided chamber this fall.

The Associated Press will declare winners in both the Democratic and Republican primaries for Maryland’s U.S. Senate seat once it can determine that a trailing candidate can’t close the gap and overtake the vote leader.

Here are the primaries at a glance:

U.S. Senate from Maryland, Democratic primary

Candidates: Prince George’s County Executive Angela Alsobrooks, U.S. Rep. David Trone, eight others

Polls close time: 8 p.m. ET

About the race: Alsobrooks and Trone are in a competitive race for the Democratic nomination to replace Democratic incumbent Ben Cardin, who is retiring after three terms.

The contest pits candidates from the state’s two most populous counties: Montgomery and Prince George’s. Trone represents the northern portion of Montgomery County in Congress, along with all of more conservative Western Maryland. Alsobrooks is the chief executive in Prince George’s County, the state’s second most populous county and the county with the highest share of Black residents in the state. If elected, Alsobrooks would become the first Black U.S. Senator in the state’s history.

Trone is co-founder and co-owner of wine retailer Total Wine and poured more than $61 million of his own money into the race, far outspending Alsobrooks.

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Much of the state’s Democratic establishment has rallied behind Alsobrooks, namely Gov. Wes Moore, U.S. Sen. Chris Van Hollen and almost all of the state’s U.S. House delegation. She also recently won the endorsement of The Washington Post.

U.S. Senate from Maryland, Republican primary

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Candidates: Former Gov. Larry Hogan, former state Rep. Robin Ficker, five others

Polls close time: 8 p.m. ET

About the race: Hogan’s late entry into the Republican primary has given his party a rare pick-up opportunity in a usually reliable Democratic state that last sent a Republican to the U.S. Senate in 1980. The two-term governor has been a vocal critic of former President Donald Trump and briefly flirted with a presidential bid last year. While his opposition to Trump may appeal to moderates and independents in the general election, it could potentially create an opening for a candidate from the right to win over Trump supporters in the more conservative corners of the state.

Robin Ficker, a disbarred attorney and frequent candidate, hopes to be that candidate. Before Hogan entered the race, Ficker had the biggest war chest of the rest of the Republican field. He has also run television advertisements aligning himself with Trump and his policies.