The last special election before the 2018 midterms will be held in Ohio on Tuesday, and the outcome could tell us a great deal about what might happen in November.

The race is for Ohio’s 12th congressional district, an area around Columbus. Republican state Sen. Troy Balderson — who has received strong support from President Donald Trump and Vice President Mike Pence — is vying to keep the GOP’s 30-year control of this district.

Balderson, 56, is facing off against 31-year-old Democrat Danny O’Connor, a local town recorder. The race is being held to fill the seat of Republican Rep. Pat Tiberi, who announced his retirement from Congress last fall. O’Connor could become one of the youngest congressmen ever elected should he win.

According to CNN, a victory for O’Connor would mean that Democrats can hope to regain seats in districts they had previously lost. Democrats need just 23 seats to obtain the majority in the House, and speculation about a possible “blue wave” in November continues. Even if Balderson wins by a narrow margin, there may still be some hope for Democrats.

Polls for the Ohio race close at 7:30 p.m. EST on Tuesday. However, there are primaries scheduled in four other states this week: Kansas, Missouri, Michigan and Washington. Here is what you need to know for each race:

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In Kansas, polls will close at 9 p.m. EST. The state’s race for governor includes candidates like Kris Kobach, a Republican secretary of state who is being backed by Trump, and GOP Gov. Jeff Colyer, who is seeking a full term after former Gov. Sam Brownback went to work for the State Department. The three Democrats running are former Wichita mayor Carl Brewer, state senator Laura Kelly and farmer Joshua Svaty. There are also two congressional races in Kansas in a pair of GOP-controlled districts that Democrats are looking to flip in November. Alexandria Ocasio-Cortez and Bernie Sanders have voiced support for candidate Brent Welders.

In Michigan, polls also close at 9 p.m. EST. There, the Democratic primary for governor features former state Senate Majority Leader Gretchen Whitmer facing off against 33-year-old Abdul El-Sayed, a progressive author and public health expert backed by Sanders.

The GOP governor primary will see black Iraq War veteran John James face three-term Sen. Debbie Stabenow. Trump has endorsed James in this race.

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In Missouri, the polls will close at 8 p.m. EST. Sen. Claire McCaskill — who is considered one of the most vulnerable Democrats — is running for re-election against several GOP challengers. The Republican front-runner is State Attorney General Josh Hawley, whom Trump has supported. McCaskill, a two-term senator, got lucky in previous elections because her opponents proved to be very controversial. One of them was Todd Akin, a GOP candidate who was severely criticized for claiming women couldn’t get pregnant from “legitimate rape.”

There is also a race in Missouri’s First House district. Incumbent Democratic Rep. Lacy Clay is running for re-election against activist and nurse Cori Bush. This will be a closely-watched race, as experts will wonder if Bush can pull a major upset like Ocasio-Cortez did over veteran Democratic Rep. Joe Crowley in New York earlier this year.

In Washington, polls will close at 11 p.m. EST. Two major congressional races are the ones to watch: in the Eighth district, former State Senator Dino Rossi is predicted to be one of the top GOP candidates to take the seat in a state Democrats are desperately hoping to take control of in November. The Democrats facing off against Rossi are Shannon Hader, a former Center for Disease Control official, attorney Jason Rittereiser and pediatrician Kim Schrier. 

In the Ninth district, Democratic Rep. Adam Smith is facing off against democratic socialist Sarah Smith.