Supreme Court Demonstration
AFP

The US Supreme Court appeared skeptical on Thursday of Donald Trump's claim that a former president is "absolutely immune" from criminal prosecution but looked set to issue a ruling that could further delay his election subversion trial.

The historic case -- the last in the court's current term -- has far-reaching implications for executive power and the 77-year-old Trump's multiple legal entanglements as he seeks the White House again.

"We're writing a rule for the ages," said Neil Gorsuch, one of three conservative justices appointed to the nation's highest court by the former Republican president.

By even agreeing to hear the case, the Supreme Court, which has a 6-3 conservative majority, already significantly delayed the start of Trump's trial on charges of conspiring to overturn the results of the 2020 election won by Joe Biden.

Special Counsel Jack Smith filed charges against Trump in August and had pushed for a March trial start date but lawyers for the former president responded with a blizzard of motions seeking its postponement, including the "absolute immunity" claim.

Speaking to reporters before entering a Manhattan courtroom for his separate hush money criminal trial, Trump complained that the judge presiding over the New York case did not allow him to personally attend the Supreme Court hearing.

"I would have loved to have been there," the Republican presidential candidate said, adding that without immunity "you're going to become a ceremonial president."

A majority of the justices on the Supreme Court, which is expected to issue its ruling by the end of June, did not appear inclined to endorse Trump's claim that as a former president he enjoys blanket immunity from criminal prosecution.

But at least four, and possibly five, of the conservative justices did appear to favor some form of presidential immunity for what may be considered "official acts."

Chief Justice John Roberts, a conservative, said he had "concerns" with a lower court ruling on the immunity question that paved the way for Trump's prosecution.

"As I read it, it says simply, 'a former president can be prosecuted because he's being prosecuted,'" Roberts said. "Why shouldn't we either send (the case) back to the Court of Appeals or issue an opinion making clear that that's not the law?"

Sending the case back to the lower court for further review would almost certainly delay Trump's election conspiracy trial until after the November vote, when he is expected to face Biden once again.

Justice Samuel Alito, an archconservative, asked why -- without immunity -- presidents won't just pardon themselves before leaving office "from anything that they might have been conceivably charged with committing?"

Justice Clarence Thomas, another staunch conservative, asked Michael Dreeben, representing the special counsel, why there had not been any previous prosecutions of a former president.

"The reason why there have not been prior criminal prosecutions is that there were not crimes," Dreeben said.

He said granting "absolute immunity" would "immunize" former presidents from criminal liability for "bribery, treason, sedition, murder" and -- in Trump's case -- "for conspiring to use fraud to overturn the results of an election and perpetuate himself in power."

John Sauer, representing Trump, told the court that "without presidential immunity from criminal prosecution there can be no presidency as we know it."

"Every current president will face de facto blackmail and extortion by his political rivals while he is still in office," Sauer said, while conceding that an ex-president could potentially be prosecuted for what may be determined to be "private acts."

The three liberals on the court -- Sonia Sotomayor, Elena Kagan and Ketanji Brown Jackson -- pushed back hard against the notion of blanket presidential immunity.

"Wouldn't there be a significant risk that future presidents would be emboldened to commit crimes with abandon?" Jackson said.

Kagan asked whether a president who "sells nuclear secrets to a foreign adversary" should be immune from prosecution.

"How about if a president orders the military to stage a coup?"

Sauer said those hypotheticals "sound very bad" but argued that "if it's an official act, there needs to be impeachment and conviction" by Congress before a president could be criminally prosecuted.

In addition to the New York case, in which Trump is accused of paying hush money to a porn star, he faces 2020 election conspiracy charges in Washington and Georgia.

He also has been indicted in Florida for allegedly mishandling classified documents after leaving the White House.