Donald Trump’s extremist attacks on top Democrats as “the enemy from within” and talk of deploying the military against political foes if he wins the election are stark signs Trump will endanger the rule of law in America, say former US justice department officials and scholars.

Trump’s threats – singling out ex-speaker Nancy Pelosi, Adam Schiff and others as “the enemy from within” and “more dangerous than China [and] Russia” – jibe with his earlier incendiary talk of using a return to the White House to seek “revenge” against political foes led by Joe Biden. He also suggested the military could be used to quell violence at the polls from “radical left lunatics”.

Those comments, along with Trump’s adamant refusal to say clearly he will accept the election results if he is defeated, prompt critics to say Trump poses unprecedented dangers to the US constitution.

Critics call Trump’s campaign rhetoric especially worrisome since it squares with his efforts after he lost the 2020 election to falsely claim the voting was rigged, while scheming to overturn the results before a mob of his allies on January 6 attacked the Capitol as Congress was certifying the results.

Alarm about a second Trump term were heightened this month when Trump’s former chief of staff and former four-star marine general John Kelly condemned him in the Atlantic as unfit to govern and having said: “I need to have the kind of generals that Hitler had.”

Ex-justice department officials are appalled by Trump’s demonizing his political foes as “the enemy from within”, words used by the demagogic senator Joe McCarthy, and ruminating about using the military against them to exact revenge.

“Trump’s anti-democratic, authoritarian rhetoric has been ratcheted up the closer we draw to the election,” said Michael Bromwich, a former inspector general at the justice department.

“Rather than keeping a covert enemies list, he publicly names his enemies against whom he vows to take action. The implications for a Trump justice department, charged with dealing with Trump’s lust to retaliate against these enemies, are frightening to consider.”

Bromwich said: “People who take their oath to the constitution seriously have trouble wrapping their heads around someone who views the constitution and the rule of law as nuisances to be circumvented rather than a set of principles to be scrupulously honored.”

Other justice department veterans express similar worries about a second Trump term.

“Trump’s rhetoric is dangerous for two reasons. Using the powers of the presidency to go after his political rivals is an incredibly dangerous deviation from democratic norms and the rule of law,” said Barbara McQuade, a former federal prosecutor in eastern Michigan and a law professor at the University of Michigan.

“The rule of law requires that we apply the law equally to everyone, and not in retaliation for political activity or speech. Second, the military is to be used against our foreign adversaries, not our own citizens. These tactics are things we see in authoritarian regimes, not democracies. Following through on these threats would change the country as we know it.”

Fears about how Trump would rule in a second term have metastasized as former senior top officials in his first administration have gone public, labeling him a fascist and unfit to be president again.

Mark Milley, Trump’s ex-chair of the joint chiefs of staff, was in quoted in Bob Woodward’s new book calling Trump “fascist to the core”.

Kelly, too, told the New York Times that Trump met the definition of a “fascist” and “prefers the dictator approach to government”, and once said that “Hitler did some good things”.

Trump in turn attacked Kelly last Friday, calling him a “whack job” and boasting that he had fired Kelly, who was a “nutjob to start off with. These are phoney stories by a general that got fired.”

Thirteen former Trump officials signed a letter supporting Kelly’s charges and attacking Trump’s “disdain for the American military and admiration for dictators like Hitler”.

Trump’s obsession with having a military loyal to him as Hitler did, fits with a larger pattern in Trump world: Trump and his allies have made it clear that loyalty to Trump will be a prerequisite to serve in a new administration, and that moderate Republicans would not be welcome.

Critics say Trump is intent on creating an administration without the kinds of guardrails that existed with people like Kelly and Milley as checks against his authoritarian instincts, a point that is underscored by Trump’s campaign talk of using the justice department to seek “revenge” on his enemies.

That mindset was palpable when Trump told the podcast host Joe Rogan on Friday that the country faces a “bigger problem … with the enemy from within” than the North Korean dictator Kim Jong-un, and allowed that his “biggest mistake” as president was hiring “disloyal people”.

Trump’s latest incendiary claims fit too with his call in 2022 on Truth Social for the “termination of all rules, regulations, and articles, even those found in the constitution”, which he justified by citing his false claims the 2020 election was stolen.

Tim Naftali, a senior research scholar at Columbia University, said: “Trump wants a second go without any obstacles from people who will tell him what he can’t do. People who served as guardrails during his first term are now worried about what he will do if he gets a second term without guardrails. From personal experience they know that his instincts are injurious to US national security and our constitutional democracy.”

Naftali noted further that the supreme court’s much criticized ruling broadening presidential immunity “has made it easier for Trump, if he wins, to push his own people to do whatever he wants”.

“The court has made this a more permissive environment for an abusive president. If he’s re-elected, Trump can take advantage of the new permissive environment created by the supreme court which wraps his official acts in at least presumed immunity.”

Naftali’s warnings are buttressed by Trump’s repeated threats to seek revenge against his enemies, whom he has often portrayed as part of a “deep state” conspiracy against him that he claims involves a weaponized justice department waging “lawfare” against him.

Little wonder that Trump last Thursday upped his attacks on Jack Smith, the special counsel who has filed criminal charges against the former president over his election subversion efforts in 2020, and for improperly taking hundreds of classified documents with him when he left office. Trump said he would fire Smith in “two seconds” and that he should be “thrown out of the country”.

Justice department veterans voice alarm about Trump’s barrage of autocratic-style threats about seeking revenge on foes in both parties if he defeats Kamala Harris.

“For a long time, Donald Trump has been promising to use government to punish his enemies. It is shocking but not surprising that he has now adopted the language of Joseph McCarthy by labelling his likely targets ‘the enemy from within’”, said Donald Ayer, a former deputy attorney general under the former president George HW Bush.

“But this is just one more piece of his single-minded effort to divide the American people and establish his own authoritarian power by attacking the basic principles that have long united us. The American people must not let him get away with this.”

Other justice department alumni see Trump posing unprecedented dangers if he wins again.

“No one in our history has ever stressed the constitution the way Trump has,” said Ty Cobb, a lawyer who served in the Trump White House and former justice department official.

Cobb added: “The founders could not have conceived of the possibility a crippled narcissist like Trump, a court-determined rapist with dozens of criminal felony convictions, serious pending charges, some involving functional insurrection, and civil fraud liability in the hundreds of millions, could possibly be a serious presidential candidate, much less elected.”

Bromwich, too, sees the prospect of Trump in power again as frightening.

“What would a justice department staffed by senior officials willing to implement Trump’s authoritarian, unconstitutional, and retaliation-minded agenda look like? Like nothing we have ever seen: staffed by lawyers with much ambition and little principle, working for a president himself protected by the immunity from prosecution conferred by the supreme court.”