(WASHINGTON) -- It's a key question in a case that could not only set constitutional precedent but also have major consequences in the 2024 election: What is "presidential immunity" and how, if at all, does it apply to former President Donald Trump regarding his efforts to overturn his 2020 election loss?
On Tuesday, Trump's claim of "absolute immunity" from prosecution in his federal election inference case will be put to the test in arguments before the U.S. Court of Appeals for the District of Columbia Circuit.
The former president, who denies all wrongdoing, contends his actions after the election and on Jan. 6, 2021, were related not to his role as a candidate but to his official constitutional duty to "take care that the laws be faithfully executed" -- in this case to investigate alleged but unproven election fraud.
Because of that, he argues, he's protected from criminal liability. He points as well to his being acquitted in his Senate impeachment trial on charges of "incitement of insurrection" as another shield from litigation.
Special counsel Jack Smith asserts Trump "is wrong" and that his arguments "threaten to undermine democracy."
The case, which is likely to wind up back before the U.S. Supreme Court, will chart new legal ground, experts told ABC News as they broke down the history and precedent of "presidential immunity."
"These are novel issues and they're going to have to create new law," said attorney Stanley Brand, a former House of Representatives general counsel whose law firm represents several former Trump aides.
Trump has posted on social media that he will attend the Jan. 9 hearing. In the post, he also continued his claim that he was "entitled" as president to immunity, arguing he was no longer campaigning but "looking for voter fraud ... and otherwise running our country."
Here's what you need to know.
What the Constitution, framers say about 'presidential immunity'
David Schultz, a professor at the University of Minnesota and national expert in constitutional law, said there is "nothing in the text of the Constitution that speaks to immunity in one way or another."
But there is textual evidence from the Constitution's framers -- including Benjamin Franklin and Alexander Hamilton -- about how they viewed the issue.
"We have language from some framers indicating that even if there might have been some immunity while a person was president of the United States, once they've left office there's no immunity and they could be charged with the crime," Schultz said.
Such statements were used in a 2000 Department of Justice memo that found the Constitution permits a former president to be indicted and tried for the same offenses for which they were acquitted in an impeachment trial, Schultz noted.
Smith's team, in its brief to the appeals court, also cited the nation's founders. They wrote Trump's immunity claim would essentially allow presidents to act criminally to remain in office, something "the Founders did not intend and would never have countenanced."
What the courts have said so far
Trump has, in some shape or form, tried to claim immunity in nearly all the legal troubles that have come his way since leaving office and has so far been rebuffed.
In the federal election interference case specifically, U.S. District Judge Tanya Chutkan rejected Trump's motion to dismiss the case on the basis of immunity. Chutkan blisteringly wrote that whatever immunities a sitting president may enjoy, the position "does not confer a lifelong 'get-out-of-jail-free' pass."
And in a Jan. 6-related civil suit brought against Trump by some U.S. Capitol Police officers, a federal appeals court similarly ruled that the former president is not entitled to absolute immunity.
Last month, another court also shot down his attempt to claim immunity in a defamation suit brought by E. Jean Carroll.
Experts weigh in on Trump's arguments
A group of legal experts, including former Trump White House attorney Ty Cobb and former impeachment special counsel Norman Eisen, sounded the alarm over Trump's claim of "absolute immunity."
In a call with reporters last week, Eisen called the idea "abhorrent to American law" while Cobb said it was important to "emphasize that no man is above the law, that is fundamentally the American approach to freedom and governance."
University of Chicago law professor Aziz Huq told ABC News that while the questions presented are unique -- as Trump is the first sitting or former president to be criminally indicted -- he believed the arguments for immunity were "exceptionally weak."
Specifically, he was skeptical of Trump's defense that the Constitution's impeachment clause or double jeopardy shields him from liability. Huq highlighted a statement from Senate Republican Leader Mitch McConnell, who said during Trump's second impeachment trial that "impeachment was never meant to be the final forum for American justice."
"We have a criminal justice system in this country," McConnell said at the time. "We have civil litigation. And former presidents are not immune from being held accountable by either one."
Brand, on the other hand, said he thought Trump could have success when it comes to arguing some of his conduct fell within the "outer perimeter" of his official duties -- a phrase Trump's team has focused on from a 1982 Supreme Court ruling involving Richard Nixon and questions of immunity. In that case, the court ruled presidents can’t be held liable in civil cases for actions they undertook as part of their official duties, though it said nothing of criminal cases after a president leaves office.
"It's complicated," Brand said. "Some of the things that are actually alleged, I think, could be conceived by a court as coming within his privilege. And while that might not require the dismissal of the entire case, it could wind up paring the evidence and some of the allegations."
One thing both experts agreed on is that timing is critical to resolve the issue before the November election.
Brand said he didn't see the issue getting resolved by March 4, which is currently the trial's start date.
Smith tried to fast-track the case by asking the Supreme Court to weigh in on the immunity question but the justices declined to take it up on an expedited basis, instead sending it to the appeals court first.
"There is almost never a stop clock running in the background, and that makes this case very different from any other criminal case," Huq said.
ABC News' Katherine Faulders and Alexander Mallin contributed to this report.