President Donald Trump's campaign to politically punish Republicans who stand in his way moves through Indiana on Tuesday, when seven state senators face Trump-backed primary challengers.

LIVE RESULTS: Indiana state primaries

In neighboring Ohio, primaries for U.S. Senate and governor will lock in the candidates for two major races with national implications.

LIVE RESULTS: Ohio state primaries

And in Michigan, voters in a bellwether district will fill a vacancy in the state Senate, a race with implications for the balance of power in a battleground state.

Here's what to watch for.

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How strong is Trump's grip on the Republican Party?

Trump is taking aim at seven Republican state senators in Indiana who opposed his plan to redraw congressional district boundaries to help the party gain seats in the U.S. House.

Groups allied with the president have spent millions on advertising, an extraordinary flood of cash and attention into races that are typically low profile.

The races are a test of Trump's enduring grip over his party as Republicans grow increasingly anxious about the midterm elections in November.

READ MORE: Trump's influence tested in Indiana primaries after failed redistricting push

The results will signal to Republicans everywhere about how big a price they'll pay with their voters if they distance themselves from Trump even as his popularity fades. And it will show the president whether he can still credibly threaten consequences for Republicans who cross him.

The Trump-targeted state senators all represent districts he carried in 2024, mostly by 20 percentage points or more.

The key races to watch are districts 1, 11, 19, 21, 23, 38 and 41.

Ohio races get started in earnest

The state's primary is the wind up to the big show. Although Ohio has become increasingly conservative, Democrats believe their path back to a U.S. Senate majority runs through the state.

They're putting their hopes behind former Sen. Sherrod Brown, who lost Ohio's other Senate seat to Bernie Moreno in 2024.

He's expected to face off with Republican Sen. Jon Husted, who was appointed last year to fill the vacancy created when JD Vance became vice president.

The race is a special election to fill the last two years of Vance's term.

WATCH: Tamara Keith and Amy Walter on redrawing congressional maps and testing Trump's power

In the campaign for governor, Republican Vivek Ramaswamy has parlayed his national name recognition, tech industry connections and alliance with Trump into a record fundraising haul. He's largely ignoring Republican rival Casey Putsch, focusing his rallies and television ads on the general election.

An engineer and vehicle designer who calls himself "The Car Guy," Putsch has attracted fans with provocative YouTube videos that troll Ramaswamy and criticize national Republicans over their handling of the Epstein files, positions on energy-guzzling data centers and support for Israel.

Amy Acton, Ohio's former public health director, is running unopposed for the Democratic nomination. She played a key role in the state's response to the COVID-19 pandemic.

Will Democrats sweep another special election?

The special election for a state Senate seat in central Michigan carries outsized importance.

It's another test of enthusiasm in a series of special elections that have swung almost universally toward Democrats since Trump returned to the White House. It also could affect the balance of power in the Michigan State Capitol. A Democratic victory would give the party a firm majority in the state Senate, while a Republican win would deadlock the chamber in a 19-19 tie.

The district is closely matched. Democrat Kamala Harris beat Trump there by less than 1 point in the 2024 presidential election.

The seat has been vacant for more than a year, since Democrat Kristen McDonald Rivet resigned to take a seat in Congress.

Democrats are showing surprising strength in special elections and off-year contests across the country, winning races in unexpected places and significantly narrowing the gap, even when they fall short.

There's no guarantee the trend will continue through the midterms, when turnout will be much higher, but it has nonetheless energized Democrats and spooked Republicans worried about keeping their congressional majorities.