Grim predictions also came from top Republican Trump critic Liz Cheney, who said that the country is "sleepwalking into dictatorship" and that she is weighing a third-party presidential run of her own to try to stop him.
Together, they paint a bleak picture of an angrier yet more disciplined Trump than during his first spell in the White House, one who would wreak vengeance on his perceived enemies and possibly try to stay in power beyond the two-term US limit.
Trump, 77, responded to the warnings in typical style by laughing them off -- with an edge.
"He says, you're not going to be a dictator, are you? I said no, no, no -- other than day one," Trump said when asked in a televised Fox News townhall on Tuesday if he would abuse power or seek retribution.
"We're closing the border and we're drilling, drilling, drilling (for oil). After that I'm not a dictator."
- 'Day one' -
President Joe Biden, who is behind Trump in the polls ahead of a likely replay of their bitter 2020 contest, said the warnings backed his own claims to be defending democracy.
"If Trump wasn't running, I'm not sure I'd be running. But we cannot let him win," the 81-year-old Democrat told a campaign event in Massachusetts.
Biden cited Trump's own increasingly violent language on the campaign trail, saying his rival's description of his opponents as "vermin" echoed the language used in Nazi Germany.
The most eye-opening piece appeared in The Washington Post by conservative commentator Robert Kagan, with the headline: "A Trump dictatorship is increasingly inevitable. We should stop pretending."
Comparing him to the power-grabbing Roman emperor Julius Caesar, the lengthy article says neither the US Constitution nor the Supreme Court could prevent Trump being "president for life" if he wanted.
Kagan wrote that if Trump survives the trials he faces over trying to upend the 2020 election and cling to power illegally, and wins the next election, he will in effect feel he is above the law and can get away with anything.
The New York Times analyzed the ways that a "second term could unleash a darker President Trump" than in his chaotic first presidency from 2017-2021.
Trump has "spoken admiringly of autocrats for decades" and would likely follow their example by packing the civil service with loyalists and using the Justice Department to crack down on opponents, it said.
In scenes reminiscent of a dystopian movie, it said Trump would also set up migrant detention camps and use the military against protesters under the US Insurrection Act.
The Atlantic magazine meanwhile is dedicating its entire January-February 2024 issue to what a Trump presidency would look like, with an editor's note titled simply: "A Warning."
- 'Dangerous moment' -
Some of the most dire forebodings have come from Liz Cheney, the former Republican lawmaker and daughter of ex-vice president Dick Cheney, whose opposition to Trump made her a pariah in the party.
"It's a very dangerous moment," she told NBC on Sunday.
There was "no question" Trump would try to stay in office beyond 2028, she said, adding that the January 6, 2021 assault on the Capitol by supporters trying to overturn Biden's election win was merely a "practice run."
For his critics, Trump's autocratic side has long been in plain sight.
Trump already faces trial for conspiring to upend the 2020 election result, with prosecutors saying on Tuesday that evidence shows he was determined to "remain in power at any cost."
His language has turned more extreme in recent months, during which he described migrants as "poisoning the blood of our country" and suggested his former military chief should face death for treason.
But in the looking-glass world of Trump and his allies, he is always the victim.
"Joe Biden is the real dictator," Trump said in a picture posted on his conservative Truth Social network.
