Former Australian prime minister Malcolm Turnbull says Donald Trump is a “relentless gaslighter” with a “powerful narcissistic self-belief”, and the best way to deal with such a “bully” is to stand up to him.

In an article for the journal Foreign Affairs, Turnbull offered advice to world leaders who may have to face Trump’s return to the White House in 2025.

Turnbull said people were deluded if they thought Trump 2.0 – who is now a convicted felon after being found guilty in his hush-money trial – would be “less volatile and alarming than the first”.

“Like most people, Trump is often wrong. Unlike most people, however, he is never in doubt,” wrote Turnbull.

“A powerful narcissistic self-belief has given him the strength to defy not just his many enemies but even reality itself.

“For four years, he has denied the outcome of the 2020 election and persuaded most of his party, and millions of Americans, to agree with him.

“There has never been such an effective and relentless gaslighter.”

Turnbull said if Trump returned to the White House, his instinct to “crush critics and stack the executive branch with yes men” would likely get even stronger.

“Trump will feel as invincible in his triumph as a Roman emperor, but he won’t have a slave by his side whispering, ‘Remember, you are mortal’.”

Turnbull said other world leaders, especially those of countries that are close US allies, would have an opportunity and a responsibility to speak to Trump with a “blunt but respectful candour”.

“Around the world, leaders are once again fretting about how they can flatter Trump and avoid his wrath.

“But that pliant approach is not just the wrong strategy; it is the last thing the United States needs.

“My own experience with Trump, when I was prime minister of Australia, is that he may not like strength and directness from other leaders, but after his rage subsides, he respects them for it.”

Revealing private conversations from his dealings with Trump when Turnbull was PM, the former Liberal leader said Trump was like “most bullies”.

“He will bend others to his will when he can, and when he cannot, he will try to make a deal. But to get to the deal-making stage, Trump’s counterparts have to stand up to the bullying first,” wrote Turnbull.

“The only way to win the respect of people such as Trump is to stand up to them.”

• Read the full transcript of the Turnbull-Trump phone call

Turnbull highlighted an example from an infamous conversation with Trump in 2017 after he had been told by a White House adviser not to ask the newly elected president to honour an agreement to settle Australia’s asylum seekers in the US.

“I did raise the issue. On the call, I told Trump that Australia expected the United States to stick to its word. Trump was furious, raging that the deal was a terrible one, that it would kill him politically, that Obama had been a fool to do it,” wrote Turnbull.

“It was daunting to be yelled at by the president of the United States, but I stood my ground.

“By the end of the call, Trump had, with great reluctance, agreed to go along with it.

“He ended by telling me it was the most unpleasant call he had had that day. A call to Putin, on the other hand, had been pleasant by comparison, he said.”

Trump unfit for office: Biden

US President Joe Biden has warned Trump would pose a higher threat to the US as a “convicted felon” if he wins a second term.

“For the first time in American history, a former president that is a convicted felon is now seeking the office of the presidency,” Biden told a small group of donors at a fundraiser in Greenwich, Connecticut on Tuesday (AEST).

“But as disturbing as that is, more damaging is the all-out assault Donald Trump is making on the American system of justice,” he said.

A Reuters/Ipsos poll last week found 10 per cent of Republican voters said they are less likely to vote for Trump in November’s presidential election following his conviction.

Biden’s comments offer a glimpse into how he and his campaign could use Trump’s conviction to make the case to voters Trump is unfit for office – an issue that could help define the presidential race by pushing Trump’s felonies to the centre of the election.

Trump still faces criminal charges in three other cases: A Georgia election interference case, a Florida documents case and a federal election interference case.

He is also appealing against the results of his civil trials.

-with AAP