WASHINGTON (AP) — A special election in a small Michigan swing district on Tuesday could have outsized consequences, determining whether Democrats retain their slim majority in the state Senate for the final months of Gov. Gretchen Whitmer's term.

Democrat Chedrick Greene and Republican Jason Tunney are vying for the 35th state Senate district seat left vacant in January 2025. Also running is Libertarian candidate Ali Sledz. The district is located about 100 miles (160 kilometers) north of Detroit and includes Saginaw, Bay City and Midland.

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Whitmer, a Democrat, is term-limited, setting up a competitive race in November to succeed her. With Democrats currently controlling the state Senate 19-18, Tuesday's outcome will be key for the state's legislative agenda in the months before she leaves office in January.

Beyond the immediate stakes, political insiders are watching the race for clues about November's midterms in this battleground state. The district includes part of Saginaw County, the only Michigan county to back the winning presidential candidate in each of the past five national elections.

"It's really this microcosm of the Midwest, frankly," said Democratic U.S. Rep. Kristen McDonald Rivet of the seat she left upon entering Congress. "Given how much it resembles so many other places across the country, we have to look at it and say, this is an indicator of how things are going to go in November."

Greene is a fire captain and Marine veteran who campaigned on lowering costs while emphasizing his union backing. Tunney, a former prosecutor, has run as a conservative Republican, highlighting his local roots in Saginaw.

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Republicans also have made the timing of the special election a central issue, arguing Whitmer, a Democrat, waited too long to call it — leaving the district without representation in the state Senate for nearly 500 days.

A victory by Greene would keep Democrats in the majority. If Tunney wins, the Senate would be tied, making it tougher for Democrats to advance their agenda. While Democratic Lt. Gov. Garlin Gilchrist II would serve as the tiebreaking vote, Republicans could effectively block any measure from passing by not having all members vote. The Michigan House is controlled by Republicans.

The term at play in Tuesday's special election is only through the end of the year, meaning the seat will again be up for reelection in November. Nonetheless, the race is being watched as a test of voter sentiment ahead of the midterm elections, when Democrats are looking to regain power in Congress.

Some strategists caution against overinterpreting the results, noting heavy Democratic spending and high-profile visits by such figures as former Transportation Secretary Pete Buttigieg and Michigan Sen. Elissa Slotkin. The Democratic Legislative Campaign Committee said in February that the special election would "set the tone for midterms" while announcing a $250,000 investment to help Michigan Democrats retain their Senate majority in May and November.

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"This is a tough race to win in any environment, but they've stacked the deck with the spending. And you layer the overall political environment on top of it, it's going to be tough," said Jason Roe, a Republican strategist in the state.

Although Republican Donald Trump carried all three counties in the 2024 presidential race, the portions of the counties that fall within District 35 are more competitive. McDonald Rivet won the seat in 2022 with 53% of the vote. Democrat Kamala Harris barely edged Trump in the district in 2024, 49.7% to 48.9%, on the strength of her 17-percentage-point lead in the Saginaw portion of the district.

Once a hub of the auto industry, the region includes a large share of union-affiliated voters and a sizable Black population, surrounded by more conservative rural areas.

Cory Smidt, interim director at Michigan State University's Institute of Public Policy and Social Research, said the district "looks like the state as a whole." Though he cautioned against viewing the outcome as a clear signal for the midterms, he said turnout and voting patterns among different groups could offer valuable insights.

Associated Press reporter Robert Yoon contributed from Washington.