Kamala Harris said Wednesday that recently reported comments Donald Trump made to his longest-serving chief of staff offer a window into who the former president "really is" and the kind of commander-in-chief he would be.

In interviews with The New York Times and The Atlantic published Tuesday, John Kelly warned that the Republican nominee meets the definition of a fascist, and that while Trump was in office, he suggested that Nazi leader Adolf Hitler "did some good things."

Harris repeated her increasingly dire warnings about Trump's mental fitness and his intentions for the presidency.

"This is a window into who Donald Trump really is, from the people who know him best, from the people who have worked with him side by side in the Oval Office and in the situation room," Harris told reporters outside the vice-president's residence in Washington.

The comments from Kelly, the retired Marine general who worked for Trump in the White House from 2017 to 2019, build on past warnings from former top Trump officials as the election enters its final two weeks.

WATCH | Trump and Harris campaign in key states: 

Trump and Harris campaign in battleground states

On Monday, Donald Trump was in North Carolina, where he insulted his Democratic opponent and made false claims about the Biden administration diverting disaster-relief funds. Meanwhile, Kamala Harris joined forces with Republican Liz Cheney to appeal to moderate voters.

Kelly has long been critical of Trump and previously accused him of calling veterans killed in combat "suckers" and "losers." His new warnings emerged as Trump seeks a second term vowing to dramatically expand his use of the military at home and suggesting he would use force to go after Americans he considers "enemies from within."

"He commented more than once that, 'You know, Hitler did some good things, too,'" Kelly recalled to the Times. Kelly said he would usually quash the conversation by saying "nothing [Hitler] did, you could argue, was good," but that Trump would occasionally bring up the topic again.

'He wants a military that is loyal to him': Harris

In his interview with the Atlantic, Kelly recalled that when Trump raised the idea of needing "German generals," Kelly would ask if he meant "Bismarck's generals," referring to Otto von Bismarck, the chancellor who oversaw the unification of Germany. "Surely you can't mean Hitler's generals," Kelly recalled asking Trump. To which the former president responded, "Yeah, yeah, Hitler's generals."

Trump's campaign denied the accounts. Campaign spokesperson Steven Cheung said Kelly had "beclowned himself with these debunked stories he has fabricated."

Harris said Wednesday that Trump admired Hitler's generals because he "does not want a military that is loyal to the United States Constitution, he wants a military that is loyal to him. He wants a military who will be loyal to him personally."

Polls show the race is tight in swing states, and both Trump and Harris are crisscrossing the country making their final pitches to the sliver of undecided voters.

Harris's campaign has spent considerable time reaching out to independent voters, using the support of longtime Republicans such as former Rep. Liz Cheney and comments like Kelly's to urge past Trump voters to reject his candidacy in November.

Harris's campaign held a call with reporters Tuesday to elevate the voices of retired military officials who highlighted how many of the officials who worked with Trump now oppose his campaign.

"People that know him best are most opposed to him, his presidency," said retired Army Brig.-Gen. Steve Anderson.

Anderson said he wished Kelly would fully back Harris over Trump, something he has yet to do. But retired Army reserve Col. Kevin Carroll, a former senior counsellor to Kelly, said Wednesday that the former top Trump official would "rather chew broken glass than vote for Donald Trump."

Kelly said Trump meets definition of fascist

Before serving as Trump's chief of staff, Kelly worked as the former president's secretary of homeland security, where he oversaw Trump's attempts to build a wall along the U.S.-Mexico border.

Kelly was also at the forefront of the Trump administration's crackdown in immigration policy that led to the separation of thousands of immigrant parents and their children along the southern border. Those actions made him a villain to many on the left, including Harris.

When Kelly joined the board of a company operating the nation's largest detention center for unaccompanied migrant children, Harris wrote during her 2019 run for president that he "was the architect of the Trump Administration's cruel child separation policy. Now he will profit off the separation of families. It's unethical. We are better than this."

When she was in Miami for a primary debate in June 2019, Harris was also one of a dozen Democratic presidential candidates who journeyed south of Miami to the detention centre. There, they protested against the Trump administration's harsh treatment of young migrants, including calling out Kelly for serving on the board of the company behind the site in Homestead, Fla., after he left the Trump administration.

In his interview with the Times, Kelly also said Trump met the definition of a fascist. After reading the definition aloud, including that fascism was "a far-right authoritarian, ultranationalist political ideology and movement characterized by a dictatorial leader," Kelly concluded Trump "certainly falls into the general definition of fascist, for sure."

Kelly added that Trump often fumed at any attempt to constrain his power, and that "he would love to be" a dictator.

"He certainly prefers the dictator approach to government," Kelly told the Times.

"I think he'd love to be just like he was in business — he could tell people to do things and they would do it, and not really bother too much about whether what the legalities were and whatnot."

Kelly is not the first former top Trump administration official to cast the former president as a threat.

Retired Army general Mark A. Milley, who served as Trump's chairman of the Joint Chiefs of Staff, told Bob Woodward in his recent book War that Trump was "fascist to the core" and "the most dangerous person to this country." And retired general Jim Mattis, who worked as secretary of defence under Trump, reportedly later told Woodward that he agreed with Milley's assessment.