As Donald Trump begins another campaign for the presidency, his extremist rhetoric and lies about the 2020 election signal that in a second term, Trump would attempt to thwart the rule of law at the justice department and other agencies in an effort to expand his power and attack critics.

Former DoJ officials, some Republicans and academics say that if Trump becomes the Republican nominee and is elected again in 2024, he would most likely appoint officials who would reflexively do his bidding, target dissenters he deems part of the “deep state” and mount zealous drives to rein in independent agencies.

Donald Ayer, a former deputy attorney general during the George HW Bush administration, told the Guardian: “Of all the many reasons Donald Trump’s candidacy should be rejected out of hand, none is more important than his utter disdain for the rule of law – the the idea that we are a society governed by rules and not by the will of one person.”

Ayer said: “It’s hard to imagine what would become of our legal system if Trump became president again.

“In his first term, aided by attorney general William Barr, who made a pretense of believing in even-handed justice, Trump was still able to grossly misuse the Department of Justice as a political campaign tool, to do favors for his friends, and to seriously undermine the separation of powers.

“There would be no arguable adults in the room in a second Trump DoJ. Beyond pardons for the January 6 criminals and politically motivated prosecutions, one can expect a broader pattern of abuse aimed at securing his autocratic power.”

Trump has given plenty of hints about what he would do in a second term, many of which suggest he would become more extreme than during his previous four years in office.

In the wake of his loss to Joe Biden in 2020, Trump falsely claimed the election was rigged and, with help from key allies, he tried to overturn the results in several states Biden won. Separately, after leaving Trump’s office retained classified documents. These Trump moves have sparked federal and state criminal investigations, which could result in charges against him and others in coming months. Trump has vehemently denied any wrongdoing in all these matters.

At campaign stops in Texas, New Hampshire and elsewhere, Trump has demonized critics, including the prosecutors leading these criminal inquiries, and spoken of the inquiries in conspiratorial terms.

During a March rally in Waco, Texas, Trump lashed out at the “thugs and criminals who are corrupting our justice system” before denouncing prosecutors and investigators. Ominously, he warned the crowd: “When they go after me, they’re going after you.”

He said: “Together, we are taking on some of the most threatening forces and vicious opponents we people have ever seen, some of them from within.”

As part of his dark Waco messaging, Trump added: “Either the deep state destroys America, or we destroy the deep state.” One of the targets of Trump’s ire has been the Manhattan district attorney, Alvin Bragg, who charged him earlier this year with 34 counts of falsifying business records to conceal hush money payments he allegedly made to the porn star Stormy Daniels. Daniels claims she had an affair with Trump in 2016.

Similarly, at the CNN town hall in New Hampshire in early May, Trump doubled down on his claims that the 2020 election was stolen from him. He also seemed to glorify the mob of loyalists who attacked the Capitol on January 6, 2021, which led to the deaths of nine police officers and others.

In an appeal to his base, Trump said that if he gets re-elected, he will be “inclined” to pardon “many” of the protesters involved in the insurrection during Joe Biden’s certification by Congress. He even called January 6 “a beautiful day”.

Given these comments on the campaign trail and his past performance in office, Trump’s critics in second terms would mean few, if any, checks on Trump’s impulsive behavior, and that he would surround himself with pliant allies.

“Donald Trump has no regard for our institutions,” the ex-DoJ inspector general Michael Bromwich told the Guardian. “There is no better proof of this general truth than his attitude towards the Department of Justice. He believed it should be the political tool of the White House, which should target his enemies and go easy on his friends.”

Bromwich noted that Trump’s choices of Barr and Jeff Sessions as attorneys general ultimately disappointed him, “because there came a point for both of them that they couldn’t go as far as Trump needed”.

“If Trump were re-elected, we can look forward to a swift and deep decline in the rule of law,” Bromwich said. “Top levels of the DoJ would be staffed with election deniers; there would be a wholesale exodus of talented career personnel from every division of DoJ; and large numbers of January 6 insurrectionists would be pardoned. After four more years, the Department of Justice as we know it would be in tatters.”

Bromwich stressed too that “Trump doesn’t believe in any type of oversight, whether conducted by Congress or inspectors general”, and that voters “should expect total resistance to any congressional oversight and the firing of IGs who dared to do their jobs of ferreting out waste, fraud, abuse and misconduct”.

Steven Levitsky, a professor of government at Harvard and the co-author of How Democracies Die, said Trump was an even more extreme candidate now than he was in his previous campaign.

“It’s pretty clear that Trump will come in as a more dangerous figure than in 2016. He had no inclination then to respect the rule of law. He saw the state as subordinate to his own will, much like a tinpot dictator. He came in as an authoritarian figure but with no plan,” Levitsky said.

“Trump filled his government mostly with conservatives who cared about not breaking the law. They provided some resistance. Civil servants and people he appointed put the brakes on his wildest instincts. Now, he’s angry and bent on revenge. Trump’s got people he wants to go after, as well as the so-called deep state. He’s going to be much more careful in the people he appoints. Trump has a much more authoritarian plan.”

The prospect of a more authoritarian President Trump is one that scares other critics who say his conduct in his first term was, at least in part, checked by conservative figures such as his ex-chief of staff John Kelly, and former secretary of state Rex Tillerson. Notably, both have voiced their opposition to Trump since they left their posts.

Kelly told the Washington Post that Trump’s pardon pledges for the January 6 rioters were not surprising: “All those people who tried to overturn the election, that’s exactly what he wanted them to do. He can’t be turning his back on the people who tried to save him in the election,” he said.

Trump has displayed other troubling signs, including allying himself with some of the most extremist Republican figures. One such person is Ken Paxton, the Texas attorney general who tried to help Trump reverse his loss to Biden. In late May, Trump used his media platform Truth Social to attack the GOP-controlled Texas House for impeaching Paxton over bribery and other alleged misconduct. The ex-president labeled Paxton’s impeachment the work of “radical left Democrats” and “Rinos” [Republicans in name only].

In another radical Truth Social post shared in late May, Trump pledged that on his first day in office he would issue an executive order to overturn birthright US citizenship – a right guaranteed in the 14th amendment.

Former GOP House member Charlie Dent told the Guardian he believed that “Trump would engage in more conduct through” executive orders upon re-election, and would “use his powers to do executive actions and ignore congressional powers and prerogatives”.

Dent predicted that in a second term, “Trump would load up his administration with sycophants, unlike in the first term”, adding that the kinds of conservatives who Trump tapped before, such as the defense secretaries James Mattis and Kelly, “will be gone ”.

“Trump will surround himself with people who would be disclined to offer any restraints on his worst impulses,” he said.

The conservative lawyer George Conway also issued direct warnings about a second Trump presidency.

“He’s going to manipulate the levers of government to help himself personally and to go after his enemies,” Conway said. “He’s going to turn our government into a third world government.”