Wisconsin voters have elected a Democratic-backed judge to serve on the state supreme court, according to projections, following the most expensive judicial election in US history.

Susan Crawford is on course to beat conservative rival Brad Schimel, which would keep intact the 4-3 liberal dominance of the Midwestern state's highest court.

President Donald Trump's billionaire adviser, Elon Musk, was a prominent fundraiser in the campaign and the subject of attack ads aired by Crawford's supporters. The candidates and their allies spent more than $90m (£70m).

The result is expected to have far reaching implications, going beyond just state law and potentially even affecting the balance of power in the US Congress.

Tuesday's vote was a setback for Trump, although his fellow Republicans managed to hold on to two congressional seats in Florida elections on Tuesday.

Earlier on Tuesday in a post on his Truth Social platform, Trump reiterated his support for "patriot" Schimel.

He called Crawford "one of the most Liberal Judges ever elected, which would be a DISASTER for Wisconsin", and said she had a "History of letting child molesters and rapists off easy".

Trump won Wisconsin - a crucial swing state in presidential elections - by less than a percentage point last November.

Tuesday's judicial contest was seen as a test of Musk's powerbroking. The SpaceX and Tesla boss travelled to the state to give out millions of dollars to voters who pledged to support conservative causes.

In the city of Milwaukee, which leans Democratic, officials reported a shortage of ballots on Tuesday "due to unprecedented and historic voter turnout", the city's election commission said in a statement.

"We are working diligently to replenish ballots," the statement said, advising voters to remain in the queue to cast ballots, even after polls closed at 20:00 local time.

Wisconsin separately voted on Tuesday to enshrine into the state constitution a law requiring voters to show ID to cast their ballots.

Voters were already required to show ID, but adding it to the state constitution made it harder to change in the future.

Wisconsin's Supreme Court is expected to play a key role in several upcoming cases, including laws around abortion and congressional redistricting ahead of the Midterm elections in 2026 and the next presidential election in 2028.