Donald Trump’s second White House chief of staff tried to stop him praising Adolf Hitler in part by trying to convince the then president that Benito Mussolini, the Italian fascist dictator, was “a great guy in comparison”.

“He said, ‘Well, but Hitler did some good things,’” the retired marine general John Kelly told Jim Sciutto of CNN in an interview for a new book.

“I said, ‘Well, what?’ And he said, ‘Well, [Hitler] rebuilt the economy.’ But what did he do with that rebuilt economy? He turned it against his own people and against the world. And I said, ‘Sir, you can never say anything good about the guy. Nothing. I mean, Mussolini was a great guy in comparison.”

Kelly, a retired US Marine Corps general, was homeland security secretary in the Trump administration before becoming Trump’s second chief of staff. Resigning at the end of 2018, he eventually became a public opponent of his former boss.

Sciutto is a CNN anchor and national security analyst. His new book, The Return of Great Powers, will be published on Tuesday. CNN published a preview on Monday.

Kelly told Sciutto it was “pretty hard to believe” Trump “missed the Holocaust” in his assessment of Hitler, “and pretty hard to understand how he missed the 400,000 American GIs that were killed in the European theatre” of the second world war.

“But I think it’s more … the tough guy thing.”

Trump’s liking for authoritarian leaders, in particular Vladimir Putin of Russia, is well known. His remarks to Kelly about Hitler – like his former practice of keeping a book of Hitler’s speeches by his bed – have been reported before.

But Sciutto’s recounting of his conversation with Kelly comes amid resurgent fears over Trump’s authoritarian leanings, with Trump the presumptive Republican presidential nominee despite facing 91 criminal charges and multimillion-dollar civil defeats, and having seen off attempts to disqualify him for office.

Kelly’s remarks to Sciutto were published shortly after Trump welcomed to his Florida home Viktor Orbán, the strongman leader of Hungary.

Singing Trump’s praises, Orbán said that if Trump defeats Joe Biden for re-election, the US would not “give a penny” more in aid to Ukraine in its fight against Russian invaders.

Kelly told Sciutto Trump “thought Putin was an OK guy and Kim [Jong-un] was an OK guy … to him, it was like we were goading these guys. ‘If we didn’t have Nato, then Putin wouldn’t be doing these things.’”

Trump recently said that if re-elected, he will encourage Russia to attack Nato members Trump deems not to pay enough into the alliance.

Condemning those remarks as “dumb, shameful and un-American”, Biden has sought to portray Trump as a threat to world security as well as US democracy.

Kelly told Sciutto: “The point is, [Trump] saw absolutely no point in Nato. He was [also] just dead set against having troops in South Korea, again, a deterrent force, or having troops in Japan, a deterrent force” to North Korea.

Kelly was not the only general to fill a civil role in Trump’s administration. James Mattis, also a marine, was Trump’s first secretary of defense while HR McMaster, from the army, was Trump’s second national security adviser.

Kelly told Sciutto Trump thought US generals would prove as loyal to him as German generals did to Hitler.

“He would ask about the loyalty issues,” Kelly said, but “when I pointed out to him the German generals as a group were not loyal to [Hitler], and in fact tried to assassinate him a few times, he didn’t know that.

“He truly believed, when he brought us generals in, that we would be loyal – that we would do anything he wanted us to do.”

A Trump spokesperson told CNN Kelly had “beclowned” himself and should “seek professional help”.

Kelly said: “My theory on why [Trump] likes the dictators so much is that’s who he is.

“Every incoming president is shocked that they actually have so little power without going to the Congress, which is a good thing. It’s civics 101, separation of powers, three equal branches of government.

“But in his case, he was shocked that he didn’t have dictatorial-type powers to send US forces places or to move money around within the budget. And he looked at Putin and Xi [Jinping, of China] and that nutcase in North Korea as people who were like him in terms of being a tough guy.”

On Tuesday, the Biden campaign responded to Kelly’s remarks.

A spokesperson, Sarafina Chitika, said: “Donald Trump’s praise for Hitler is disgraceful but wholly unsurprising from the man who has parroted Nazi rhetoric on the campaign trail, called his political opponents ‘vermin’, and sucked up to dictators and authoritarians like Vladimir Putin, Viktor Orbán, Kim Jong-un, and the rest of the gang.

“When Donald Trump talks like a dictator, praises dictators, and says he wants to be a dictator, we should probably believe him.”