Conservative defeats in two high-profile Midwestern elections are likely to embolden the left as the nation girds for the 2024 election cycle. 

In Wisconsin, a Democratic-backed Milwaukee judge won the high stakes state Supreme Court race Tuesday, ensuring liberals will take over majority control of the court for the first time in 15 years with the fate of the state’s abortion ban on the line.

At the Windy City, meanwhile, a union organizer and former teacher, Brandon Johnson, was elected as mayor Tuesday in a major victory for the Democratic Party’s liberal wing as the heavily blue city grapples with high crime and financial challenges.

In the Badger State, a Milwaukee County circuit judge, Janet Protasiewicz, 60, defeated a former Supreme Court justice, Dan Kelly, who previously worked for Republicans and had support from the state’s leading anti-abortion groups.

The victory speaks to the importance of abortion as an issue for Democrats in a key swing state, with turnout the highest ever for a Wisconsin Supreme Court race that didn’t share the ballot with a presidential primary.

In a jubilant scene at her victory party, the other three liberal justices on the court joined Judge Protasiewicz on the stage and raised their arms in celebration.

Judge Protasiewicz tried to downplay the importance of abortion as an issue in her victory, even though she and her allies, including an array of abortion rights groups including Planned Parenthood, made it the focus of much of her advertising and messaging to voters.

“It was really about saving our democracy, getting away from extremism and having a fair and impartial court where everybody gets a fair shot in the courtroom,” Judge Protasiewicz said after her win. 

The new court controlled 4-3 by liberals is expected to decide a pending lawsuit challenging the state’s 1849 law banning abortion enacted a year after statehood. 

Judge Protasiewicz said during the campaign that she supports abortion rights but stopped short of saying how she would rule on the lawsuit. She had called Justice Kelly an “extreme partisan” who would vote to uphold the ban.

In addition to abortion, Judge Protasiewicz’s win is likely to impact the future of Republican-drawn legislative maps, voting rights and years of other GOP policies. It will also ensure that liberals will have the majority leading up to the 2024 presidential election and immediately after.

Four of the past six presidential elections in Wisconsin have been decided by less than a percentage point and President Trump turned to the courts in 2020 in his unsuccessful push to overturn his roughly 21,000-vote loss in the state. 

The current court, under a 4-3 conservative majority, came within one vote of overturning President Biden’s win in the state in 2020, and both major parties are preparing for another close race in 2024.

Justice Kelly is a former justice who has also performed work for Republicans and advised them on a plan to have fake GOP electors cast their ballots for Trump following the 2020 election even though Trump had lost.

At Chicago, Mr. Johnson, a Cook County commissioner endorsed by the city’s teachers union, won a close race over the former city schools chief executive, Paul Vallas, who was backed by the police union. Mr. Johnson, 47, will succeed Lori Lightfoot, the first Black woman and first openly gay person to be the city’s mayor.

Mr. Johnson’s victory in the nation’s third-largest city capped a remarkable trajectory for a candidate who was little known when he entered the race last year. 

He climbed to the top of the field with organizing and financial help from the politically influential teachers union and high-profile endorsements from Senators Sanders and Warren. Mr. Sanders appeared at a rally for Johnson in the final days of the race.

Taking the stage Tuesday night for his victory speech, a jubilant Mr. Johnson thanked his supporters for helping usher in “a new chapter in the history of our city.” 

Mr. Johnson, who is Black, recalled growing up in a poor family, teaching at a school at Cabrini Green, a notorious former public housing complex, and shielding his own young kids from gunfire in their West Side neighborhood.

He referenced civil rights leaders Martin Luther King Jr. and the Reverend Jesse Jackson and called his victory a continuation of their legacies. He also noted that he was speaking on the anniversary of King’s assassination.

“Today the dream is alive,” Mr. Johnson said, “and so today we celebrate the revival and the resurrection of the city of Chicago.”

For both liberals and the Democratic party’s more moderate wing, the Chicago race was seen as a test of organizing power and messaging.

Mr. Johnson’s win also comes as groups such as Our Revolution, a powerful progressive advocacy organization, push to win more offices in local and state office, including in upcoming mayoral elections in Philadelphia and elsewhere.

Mr. Vallas, speaking to his own supporters Tuesday night, said that he had called Mr. Johnson and that he expected him to be the next mayor. Some in the crowd seemed to jeer the news, but Mr. Vallas urged them to put aside differences and support the next mayor in “the daunting work ahead.”

“This campaign that I ran to bring the city together would not be a campaign that fulfills my ambitions if this election is going to divide us,” Mr. Vallas said.

On Tuesday, Mr. Johnson took many of the predominantly Black southern and western areas where Ms. Lightfoot won in February, along with the northern neighborhoods where he was the top-vote getter back then, according to precinct-level results released by election officials. 

Mr. Vallas did well in the northwest and southwest areas that are home to large numbers of city employees, just as he did in February.

The contest surfaced longstanding tensions among Democrats, with Mr. Johnson and his supporters blasting Mr. Vallas — who was endorsed by Senator Durbin of Illinois, the chamber’s second-ranking Democrat — as too conservative and a Republican in disguise.