Two members of a three-judge panel of the 2nd US Circuit Court of Appeals in Manhattan challenged Trump's lawyer Michael Madaio during oral arguments in Trump's appeals of pivotal rulings by US District Judge Lewis Kaplan.
Madaio called presidential immunity an "absolute and nonwaivable protection" that judges could not override.
Carroll, a former Elle magazine columnist, sued Trump in November 2019 over his denial five months earlier that he had raped her in a midtown Manhattan department store dressing room in the mid-1990s. Trump, who was president in 2019, said Carroll was "not my type" and suggested that she made up the rape claim to boost sales of her forthcoming memoir.
Trump is appealing Kaplan's June 29 refusal to dismiss Carroll's lawsuit, and the judge's August 7 dismissal of some of his defences and a defamation counterclaim against her.
Kaplan ruled on September 6 that Trump's denial was defamatory, leaving only the issue of damages for the trial scheduled for January 16, 2024. Carroll is seeking at least $US10 million ($A16 million).
On May 9, another jury awarded Carroll $US5 million for sexual assault and defamation, though not rape, after Trump last October again denied that the rape occurred. Trump is also appealing that verdict.
During Monday's arguments, Madaio said Trump acted in the "outer perimeter" of his job as president by responding to Carroll's accusations. Madaio also said denying immunity would disrupt the constitutional separation of powers between the US government's executive and judicial branches.
Trump "faced an unprecedented, unprovoked attack on his character," Madaio said. "As both the leader of a nation and the head of the executive branch, he could not sit idly by."
Circuit Judge Denny Chin questioned why Trump waited until December 2022 to claim immunity, even as the former president raised other defences, after both sides had gathered evidence.
"This was litigated for three years without the assertion of the defence," Chin said. "How was it an abuse of discretion for Judge Kaplan to say it was too late?"
Carroll, 79, has long accused Trump, 77, of using stall tactics to keep her case from getting to trial. She proposed the $US10 million damages award after Trump disparaged her as a "whack job" in a CNN town hall-style event following the previous verdict.
Carroll's lawyer Joshua Matz rejected any suggestion Trump could not waive absolute immunity because "broader structural considerations" were at play.
"That is hokum," Matz told the appeals court. "A party who believes that they are holding onto absolute immunity from suit does not behave the way that Mr. Trump behaved it his case."
The appeals court did not say when it will rule.
