Wisconsin voters elected Susan Crawford to the state Supreme Court on Tuesday, The Associated Press projected, maintaining the court's 4-3 liberal majority in a setback for U.S. President Donald Trump and his billionaire ally Elon Musk, who had backed her conservative rival.

The election was widely seen as an early referendum on Trump's presidency. The campaign easily became the most expensive judicial contest in U.S. history with more than $90 million US spent by the candidates, the state parties and outside groups, according to a tally from New York University's Brennan Center.

Crawford, a county judge, defeated conservative Brad Schimel, a former Republican state attorney general and also a county judge.

With the balance of the court at stake, Musk and political groups tied to him spent more than $21 million US to support Schimel.