Madison, Wisconsin - Donald Trump was dealt the first serious blow of his second term as Wisconsin voters rejected far-right billionaire Elon Musk's efforts to sway the state's supreme court race and elected the liberal candidate.

Two months into his barnstorming return to the White House, Trump celebrated victory in a pair of House elections in Florida which remained in Republican hands.

But in the first real electoral test of his presidency, his all-out effort to lodge a new Republican on the Wisconsin Supreme Court fell flat, as liberal judge Susan Crawford came out ahead of Trump-backed Brad Schimel.

Trump appeared to ignore the results on social media, highlighting a separate Wisconsin ballot initiative requiring voters to present photo identification to cast a ballot.

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"Voter I.D. just approved in Wisconsin election...this is a big win for Republicans, maybe the biggest win of the night," he posted on TruthSocial late Tuesday.

Elon Musk, who has spearheaded Trump's attempts to gut much of the US government, went to Wisconsin to drum up support for Schimel and even handed out money to anyone who signed a petition against so-called "activist judges."

He too refrained from commenting on Schimel's loss despite spending millions on the campaign, instead taking to X to post "Yeah!" on news of Wisconsin passing the voter ID initiative.

Independent Senator Bernie Sanders told supporters on X they had "the power to REJECT Musk and the oligarchy buying our elections."

In Florida, two seats in the US House of Representatives were up for grabs to fill vacancies in Republican strongholds, left by Trump's National Security Advisor Mike Waltz and failed nominee for attorney general, Matt Gaetz.

On Tuesday evening, the race for Florida's sixth district was called in favor of far-right Republican Randy Fine, who has made a name for himself by calling for the extermination of Palestinians in Gaza and making Islamophobic threats against members of Congress.

The special election in Florida's first district was also won by Trump-backed Republican Jimmy Patronis.

The president took credit for his party's victory in both deep red districts, posting on social media that "the Trump endorsement, as always, proved far greater than the Democrats forces of evil."