US President-elect Donald Trump would have been convicted for his alleged effort to overturn the 2020 election result if he hadn't been re-elected four years later, said a report by then special counsel Jack Smith released early Tuesday.

In a case that never went to trial, Trump, who returns to the White House on Monday, was accused of conspiracy to defraud the United States and conspiracy to obstruct an official proceeding.

However, the US Department of Justice's "view that the Constitution prohibits the continued indictment and prosecution of a President is categorical and does not turn on the gravity of the crimes charged, the strength of the Government's proof, or the merits of the prosecution, which the Office stands fully behind," said the report, which was released after midnight.

"Indeed, but for Mr. Trump's election and imminent return to the Presidency, the (Special Counsel's) Office assessed that the admissible evidence was sufficient to obtain and sustain a conviction at trial."

The proceeding referred to in the charges was the session of Congress called to certify President Joe Biden's election win that was violently attacked on 6 January 2021, by a mob of Trump's supporters who stormed the US Capitol.

Smith, who was special counsel appointed to investigate Trump, dropped the case after the Republican won November's presidential election, citing the Justice Department's policy of not prosecuting a sitting president.

Trump, 78, hit back on his Truth Social platform soon after the report's release, calling Smith "deranged," and adding that he "was unable to successfully prosecute the Political Opponent of his 'boss.'"

"To show you how desperate Deranged Jack Smith is, he released his Fake findings at 1:00 AM in the morning," Trump added in another post.

Trump's attorneys had earlier urged US Attorney General Merrick Garland not to release the report, calling the plan to disclose it "unlawful, undertaken in bad faith, and contrary to the public interest."

Change the results

Smith's report details Trump's alleged efforts to persuade state-level Republican lawmakers and leaders to "change the results" of the 2020 election.

"Mr. Trump contacted state legislators and executives, pressured them with false claims of election fraud in their states, and urged them to take action to ignore the vote counts and change the results," according to the report released by the Department of Justice.

"Significantly, he made election claims only to state legislators and executives who shared his political affiliation and were his political supporters, and only in states that he had lost," it said.

In addition, the report alleges Trump and co-conspirators planned to organize individuals who would have served as his electors, if he had won the popular vote, in seven states where he lost — Arizona, Georgia, Michigan, Nevada, New Mexico, Pennsylvania and Wisconsin — "and cause them to sign and send to Washington false certifications claiming to be the legitimate electors."

They ultimately "used the fraudulent certificates to try to obstruct the congressional certification proceeding," the report says, adding that Trump had "engaged in an unprecedented criminal effort" to overturn the election results "in order to retain power."

The report says Trump's untruths included dozens of demonstrably false claims that large numbers of ineligible voters, such as non-citizens, had cast ballots, and that voting machines had changed votes that had been for him.

Trump, however, knew there was no fraud that would affect the election's outcome and that he had lost, according to the report, in part because then vice-president Mike Pence and his advisers told him there was no evidence for his claims.

The report says that, on 2 January 2021, days before election tallies would be certified, Trump called Georgia's secretary of state and pushed him to "find 11,780 votes" — Biden's margin of victory in the southern state.

When the state official refuted Trump's false claims, the then-president threatened him, the report says.

Trump faces separate racketeering charges in Georgia over his efforts to subvert the election results in the state. That case will likely be frozen while he is in office.

The special counsel office concluded that "Trump's conduct violated several federal criminal statutes and that the admissible evidence would be sufficient to obtain and sustain a conviction."

Judge Aileen Cannon, a Trump appointee, dismissed another federal case against the former and future president last year — over Trump's handling of top secret documents after leaving the White House — but charges are still pending against two of his former co-defendants.

Smith left the justice department last week, days after submitting his final report as special counsel.

In another case, a judge sentenced Trump to an unconditional discharge on Friday for covering up hush money payments to a porn star despite the president-elect's efforts to avoid becoming the first felon in the White House.