The last time Wisconsin held an election for the state’s Supreme Court, Republicans cried foul over the wave of money from out-of-state Democrats that overwhelmed their candidate.

Two years later, Republicans have learned their lesson. It is Democrats who are grappling with a flood of outside money inundating Wisconsin.

A super PAC funded by Elon Musk has in just the past week spent $2.3 million on text messages, digital advertisements and paid canvassers to remind Wisconsin Republicans about the April 1 election, which pits Brad Schimel, a judge in Waukesha County and a former Republican state attorney general, against Susan Crawford, a Dane County judge who represented Planned Parenthood and other liberal causes in her private practice.

The spending by Mr. Musk, the tech billionaire who is leading President Trump’s project to eviscerate large segments of the federal government, comes as Judge Schimel and his Republican allies have spent more money on television ads than Judge Crawford and Democrats have — a remarkable turnaround in a state where Democrats have had a significant financial advantage in recent years.

“When I was a little girl growing up in Chippewa Falls, I never could have imagined that I’d be fighting the world’s richest man,” Judge Crawford told a crowd over the weekend at a campaign stop in Cambridge, Wis.

As of Monday, Republicans had spent or reserved $13.9 million of television advertising time for the Wisconsin court race, compared with $10.7 million for Democrats, according to AdImpact, a media-tracking firm. Because a larger chunk of Republican spending comes from super PACs, which pay a higher rate for TV ads than candidates do, the amount of advertising on Wisconsin’s airwaves has remained roughly equal. But the heavy Republican spending has eliminated what was a significant advantage for Democrats in the last such contest, in 2023.

Mr. Musk’s digital ads and literature left at Republican homes have so far been designed to remind Trump voters — who historically have been less likely than Democrats to vote outside presidential elections — to show up to vote. “President Trump needs you to get out and vote,” read one flyer, which did not mention Judge Schimel but attacked Judge Crawford.

Brian Schimming, the Wisconsin G.O.P. chairman, said Judge Schimel would likely win if 60 percent of Mr. Trump’s voters turned out for him.

The stakes of the Wisconsin race are immense, just as they were in 2023. The winning side will hold a four-to-three majority on the state high court, which is expected to render decisions about abortion, voting access, the state’s collective bargaining laws and its congressional maps.

If Judge Crawford is elected to a 10-year term, liberals will cement a majority until at least 2028. If Judge Schimel prevails, however, conservatives will control the court, with the majority up for grabs again in 2026 and 2027, when seats now held by conservative justices will come up for election.

Republicans were caught flat-footed in 2023.

Justice Janet Protasiewicz, the liberal candidate that year, spent more than four times as much as her conservative opponent, Daniel Kelly, and won by 11 percentage points, a shocking blowout by Wisconsin standards in a contest that flipped ideological control of the court for the first time in 15 years.

Though the state’s judicial races are officially nonpartisan, the Democratic Party of Wisconsin endorsed Justice Protasiewicz, while Mr. Kelly, a former state Supreme Court justice who had lost a re-election bid in 2020, refused an endorsement from the state’s Republican Party, which had very little money to give and was not trusted by conservative donors.

Democratic money flowed into the race like never before. With more than $50 million in spending, it became the most expensive judicial contest in American history. Reid Hoffman, the billionaire co-founder of LinkedIn, gave the state Democratic Party $2.5 million, which it subsequently transferred to the Protasiewicz campaign. (Mr. Hoffman gave another $7.4 million to Wisconsin Democrats in 2024, when the state was a top presidential battleground.)

The state’s campaign finance law allows donors to give unlimited sums to state parties, which in turn can transfer unlimited sums to its endorsed candidates.

Now, however, some major Democratic donors are holding on to their wallets. Mr. Hoffman, so generous in 2023, has donated a comparatively meager $250,000 for this year’s Supreme Court race at a time when he is pulling back on his political activity. Gov. JB Pritzker of Illinois, who gave $1 million for the judicial contest two years ago, has donated $500,000. (George Soros, who gave $1 million in 2023, did so again last month.)

Ben Wikler, the Wisconsin Democratic chairman, said the pace of spending for Judge Crawford was ahead of where spending was for Justice Protasiewicz in the 2023 race, largely thanks to small donations. Judge Crawford has received more individual contributions since Mr. Musk’s initial super PAC contributions last week than she did for the entire campaign up to that point, according to her campaign spokesman, Derrick Honeyman.

“Democrats across the country are wondering, ‘What the hell can I do to fight back against the lawless regime of Donald Trump and Elon Musk?’” Mr. Wikler said. “The answer to that question is to support Susan Crawford beating Brad Schimel.”

For Wisconsin Republicans, Mr. Musk’s funds are effectively granting permission to other right-wing donors to invest in the race, said Mr. Schimming, who lamented that Republicans did not nationalize the 2023 race and allowed Mr. Kelly to get swamped on the TV airwaves.

Republican donors who spurned the state party then are ponying up now. Richard and Elizabeth Uihlein, Illinois billionaires who are among the country’s most prolific conservative donors, gave $1.3 million to the party to help Judge Schimel — in addition to the $2.4 million their super PAC, Fair Courts America, has already spent on TV advertising in the race.

“The Dan Kelly race, as tragic as it was, provides us a recent example of what happens in court races when there’s not a proper amount of attention to them,” Mr. Schimming said. “Even though I’ve lived in Wisconsin my whole life, I have no problem writing thank-you notes to ZIP codes that don’t start with a five. I can do it all day long.”

Mr. Kelly, for his part, said in an interview Tuesday that he had “no regrets” about his 2023 campaign and lamented the influence of millions of dollars flowing through the political parties to favored Supreme Court candidates.

“I’m very uncomfortable with political parties making large contributions to judicial candidates,” he said. “When you see these unlimited political contributions, I don’t know how people are supposed to believe that politics is not going to play a role in what the court does.”