The US Supreme Court has handed a major legal victory to Donald Trump, with a blockbuster ruling that ex-presidents are partially immune from criminal prosecution.

In a divided 6-3 ruling, the court said former presidents could be shielded from prosecution for “official” acts within their constitutional authority, but not private acts.

It’s the first time since the US was founded that the Supreme Court has declared ex-presidents may be immune from criminal charges in any instance.

The ruling means it is unlikely that Trump will go to trial on charges relating to the January 6 attack on the US Capitol before this year’s presidential election.

Trump, 78, welcomed the decision in a post written in capital letters on his platform Truth Social: “Big win for our constitution and democracy.”

Trump has hailed the victory on his Truth Social.

The Republican candidate is the first former US president to be criminally prosecuted as well as the first to be convicted of a crime.

The court’s 6-3 conservative majority included three justices Trump appointed and three liberal justices who dissented strongly and expressed “fear for our democracy”.

Justice Sonia Sotomayor warned that “the president is now a king above the law”.

The court threw out an earlier judicial decision that had rejected Trump’s bid to shield himself from charges involving his efforts to overturn his 2020 election loss.

Trump had appealed that lower court ruling, arguing he was immune from prosecution because he was president when he took the actions that led to the charges.

Special Counsel Jack Smith, who brought the charges, had opposed presidential immunity from prosecution based on the principle that no one is above the law.

In Smith’s August 2023 indictment, Trump was charged with conspiring to defraud the US, corruptly obstructing an official proceeding and conspiring to do so, and conspiring against the right of Americans to vote. He has pleaded not guilty.

Trump’s trial had been scheduled to start on March 4 before the delays over immunity.

Now, there is no trial date. Trump made his immunity claim to the trial judge in October, meaning the issue has been litigated for about nine months.

In a separate case brought in New York state court, Trump was found guilty by a jury in Manhattan on May 30 on 34 counts of falsifying documents to cover up hush money paid to a porn star to avoid a sex scandal before the 2016 election.

Trump also faces criminal charges in two other cases. He has pleaded not guilty in those and called all the cases against him politically motivated.

A lawyer for Smith’s office told the Supreme Court during arguments that the “absolute immunity” sought by Trump would shield presidents from criminal liability for bribery, treason, sedition, murder and, as in this case, trying to overturn the proper results of an election and stay in power.

During the arguments, justices asked hypothetical questions involving a president selling nuclear secrets, taking a bribe or ordering a coup or political assassination.

If such actions were official conduct, Trump’s lawyer said, a former president could be charged only if first impeached by the House of Representatives and convicted in the Senate – something that has never happened in US history.

The timeline of the court’s immunity ruling likely does not leave enough time for Smith to try Trump on federal election subversion charges and for a jury to reach a verdict before American voters head to the polls.

Trump also faces election subversion charges in state court in Georgia and federal charges in Florida brought by Smith relating to keeping classified documents after leaving office.

If Trump regains the presidency, he could try to force an end to the prosecution or potentially pardon himself for any federal crimes.

-with AAP