WASHINGTON • As president of the United States, Mr Donald Trump would wield the power to carry out his vow to have a special prosecutor reopen the investigation into Mrs Hillary Clinton's e-mail - if not to guarantee his threat that "you'd be in jail" if he ran the country.
But the move would take American democracy to a dangerous new place, legal specialists across the ideological spectrum said.
"It's a chilling thought," said Mr Michael Chertoff, who served as secretary of Homeland Security and head of the Justice Department's criminal division in the George W. Bush administration. Mr Chertoff, who said he will vote for Mrs Clinton, added: "It smacks of what we read about tin-pot dictators in other parts of the world, where when they win an election, their first move is to imprison opponents."
Early in the second presidential candidates' debate on Sunday, Mr Trump brought up the investigation into Mrs Clinton's use of a private e-mail server while she was secretary of state. That case was closed without charges, but Mr Trump said he would order it reopened.
In response, Mrs Clinton accused him of falsely describing the facts of the case, adding: "It's just awfully good that someone with the temperament of Donald Trump is not in charge of the law in our country." He shot back: "Because you'd be in jail."
Mr Trump's assertion is taking its place among other claims that many US legal specialists have portrayed as a threat to the rule of law.
"This is a manifestation of the same tendency to be willing to use the machinery of the state to go after one's political enemies, which is very dangerous," said Mr David Rivkin, a White House and Justice Department lawyer in the administration of president George H.W. Bush. He has criticised the decision to close the e-mail investigation without charges.
Special prosecutors are appointed in sensitive cases where senior officials may have a conflict of interest. Presidents can also effectively exercise ultimate authority because they can fire Cabinet officials who refuse orders. President Richard Nixon in 1973 fired the top two officials in the Justice Department because they refused to fire the special prosecutor investigating Watergate.
Professor Jonathan Adler, a Case Western Reserve University law don, noted that presidents from both parties have been centralising executive branch decisions since the 1980s, and thinks Mr Trump's threat is a further fraying of checks and balances: "The appearance of the justice system being used for partisan payback is poisonous."
Still, several conservatives critical of Mr Trump drew a parallel to a statement in 2008 by Mr Eric Holder, an adviser to then Senator Barack Obama and later the President's attorney-general. Mr Holder denounced the George W. Bush administration for failing its "commitment to the Constitution and to the rule of law" after the terrorist attacks of Sept 11, 2001, declaring that "we owe the American people a reckoning".
But Mr Obama opposed investigating Bush administration veterans for the torture of terror suspects. Mr Holder decided in 2009 on a narrower probe into whether the CIA abused detainees. However, no charges resulted.