WILLIAM BRANGHAM: As President Trump escalates his fights with federal judges, he's also bolstering a judicial candidate in the battleground state of Wisconsin.

It is a loud and expensive race that has become a fight over the president's agenda.

And, as Deema Zein reports, it's testing the limits of presidential adviser and billionaire Elon Musk's money and popularity.

DEEMA ZEIN: Across Wisconsin, a critical election that will determine who will fill a seat on the state Supreme Court for the next 10 years.

It's seen by many as an early litmus test of how voters feel about President Trump's policies in a swing state he won by nearly 30,000 votes last year, on the ballot, two current county judges both looking for a promotion.

SUSAN CRAWFORD, Wisconsin Supreme Court Candidate: Wisconsinites want a commonsense justice who will be fair and impartial.

DEEMA ZEIN: Judge Susan Crawford from Dane County, home to the state capital, Madison, and a liberal stronghold... BRAD SCHIMEL, Wisconsin Supreme Court Candidate: It's not a good look for our country.

DEEMA ZEIN: ... versus Judge Brad Schimel from Waukesha County, a conservative-leaning suburb of Milwaukee.

He's also Wisconsin's former attorney general.

Whoever wins Tuesday will determine the majority of the seven-member Supreme Court, which after 15 years in conservative control, flipped to a 4-3 liberal majority in the last election two years ago.

BARRY BURDEN, Elections Research Center Director, University of Wisconsin-Madison: The level of intensity in the state feels about like a presidential election.

DEEMA ZEIN: Barry Burden is the director of the Elections Research Center at the University of Wisconsin-Madison.

BARRY BURDEN: It's now become kind of a national referendum, or at least a way to measure the temperature of the electorate a couple of months into the Trump administration.

The fact that the court is up for grabs ideologically and is weighing in on these important issues and money is so easily spread into these campaigns has really been the kind of magic stew that has put these elections on the map for everyone.

DEEMA ZEIN: The result?

NARRATOR: Too extreme for the Supreme Court.

DEEMA ZEIN: The most expensive court election in U.S. history, with more than $90 million spent so far.

NARRATOR: Because she fights for them, not us.

DEEMA ZEIN: While the race is officially nonpartisan, the dividing lines are clear.

SUSAN CRAWFORD: This election will determine the future of our state.

DEEMA ZEIN: Crawford has support from the state Democratic Party.

BRAD SCHIMEL: I hope to have your vote.

DEEMA ZEIN: Schimel is backed by Republicans, including President Trump.

BRAD SCHIMEL: Then the call comes: "Hello, Brad.

It's your favorite president."

(LAUGHTER) PROTESTERS: Not for sale!

Not for sale!

DEEMA ZEIN: But it's the efforts by Elon Musk that are getting the most attention.

The billionaire businessman, who has spent the last two months slashing federal spending and firing federal workers in the name of government efficiency, has turned his sights to the Badger State.

NARRATOR: Susan Crawford's record disturbing and dangerous.

DEEMA ZEIN: Musk has dropped $20 million to support Schimel's campaign on ads and more direct get-out-the-vote efforts.

ELON MUSK, Department of Government Efficiency: The very important election for Judge Schimel.

DEEMA ZEIN: His political action committee offered voters $100 to sign a petition against -- quote -- "activist judges."

ELON MUSK: Let me first hand out two $1 million checks.

DEEMA ZEIN: And, on Sunday, he was in Wisconsin handing out million-dollar checks to two people.

Musk originally limited eligibility to voters, but changed it to petition signers after legal scrutiny.

The Democratic attorney general accused Musk of trying to buy votes and sued all the way to the state Supreme Court to block the giveaway, but the justices declined to step in.

BARRY BURDEN: Musk has become a pretty central figure in the campaigns.

Democrats and progressives are arguing that this election ought to be a rebuke of what Musk is doing in Washington, and they have turned it into kind of a judgment on his actions, asking voters to send a message that Musk should not be meddling in Wisconsin state politics.

Conservatives, on the other hand, have really embraced him.

SUSAN CRAWFORD: He has basically taken over Brad Schimel's campaign.

DEEMA ZEIN: Musk has become central for the candidates on the trail and in their final debate.

Musk's electric car company, Tesla, is suing to overturn a law that prevents it from opening a dealership in the state, an issue that could ultimately end up before the Wisconsin Supreme Court.

Schimel says Musk's support won't sway how he would rule.

BRAD SCHIMEL: If Elon Musk is trying to get some result in that lawsuit, he may be failing, because I enforce the law and I respect the laws passed by the legislature.

MAN: The Wisconsin State Supreme Court is now in session.

DEEMA ZEIN: The winner could have a critical vote on other issues as well.

WOMAN: Our first case this morning.

DEEMA ZEIN: Union rights, voting rules and congressional redistricting are all likely to end up at the court.

WOMAN: We're trying to figure out if medical providers here are going to be able to save women's lives.

DEEMA ZEIN: Wisconsin's current justices will soon decide the fate of an 1849 law that bans nearly all abortions in the state.

MAN: I mean, we're trying to get it right, I hope, not just get an outcome here.

DEEMA ZEIN: And while the winner on Tuesday won't have a role in that specific case, the issue still looms large in the race.

MAN: You believe the 1849 law is valid?

BRAD SCHIMEL: It was a validly passed law.

MAN: Today?

BRAD SCHIMEL: I don't believe -- I don't believe that it reflects the will of the people of Wisconsin today.

MAN: Judge, do you believe that law is valid today, the 1849 law?

SUSAN CRAWFORD: Well, Matt, this is an issue that's pending before the Wisconsin Supreme Court.

I'm not in a position to weigh in at this point.

DEEMA ZEIN: Schimel has called himself pro-life, while, as a lawyer, Crawford represented Planned Parenthood.

All those swirling issues have led to a surge in turnout at the polls.

WOMAN: Read carefully.

DEEMA ZEIN: Nearly 650,000 voters cast ballots early, up more than 40 percent from the Supreme Court election two years ago, for voters, deeply personal choices.

On abortion access.

LINDA OLIVER, Wisconsin Voter: I don't think that we should be governed by a law that was passed before the Civil War.

LEWIS TITUS, Wisconsin Voter: I believe in the sanctity of life.

And I believe that Brad Schimel is the one that's going to be able to carry that on.

DEEMA ZEIN: On larger questions about the role of judges.

CINDY SUPLINSKI, Wisconsin Voter: I was very impressed with how he is really focused on upholding the laws, not making the laws, not bringing his own personal biases into the laws.

DEEMA ZEIN: And voters' own judgments about President Trump's first few months in office.

CHRISTINA DANFORTH, Wisconsin Voter: The president is sidestepping the laws.

He's just sidestepping them.

And I don't want somebody representing the status Wisconsin that will allow that, will tolerate that.

DEEMA ZEIN: A technically nonpartisan race highlighting deep political divides.

For the "PBS News Hour," I'm Deema Zein.