The 81-year-old has nominated his vice president to replace him in the November contest against second-time presidential hopeful Mr Trump, and will remain in his role until his term officially ends in January.

Australian politicians are familiar with Ms Harris and Mr Trump, University of Sydney associate professor David Smith said, which means they already understand how the bilateral relationship might work.

“Australia is already preparing for a world after President Biden,” he told AAP.

A second Trump term could pose issues for Australian exports after the 78-year-old’s campaign began promoting protectionist policies, including large tariffs on Chinese goods, Prof Smith said.

The Republican runner’s approach to democracy both internationally and domestically has also worried some Australians.

Mr Trump has previously said he would end the war in Ukraine within 24 hours, but it’s unclear if that means pushing for Ukrainian territory to be ceded to Russia or other methods.

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His rhetoric also affects politics in other countries, with many far-right movements across the world adopting Mr Trump as their global icon.

And within the US, his attempts to undermine the 2020 outcome that evicted him from office by falsely claiming the election had been “stolen” – as well as indications he could do similar if he doesn’t win in November – also remain a concern.

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“If he loses, I think he does remain a threat to democracy,” Prof Smith said.

Former Liberal prime minister Malcolm Turnbull has urged Labor’s Anthony Albanese not to “suck up” to “bullies” like Mr Trump.

“America under Trump is a less reliable ally than it has been under Biden or other presidents,” he told ABC on Monday.

Ms Harris’ approach to foreign affairs has been relatively discrete, but her leadership is unlikely to raise similar concerns.

“She’s been one of the lowest-profile vice presidents in my lifetime … which means we don’t have any great insight into how she views the world,” Prof Smith said.

“For people in the Australian government, I don’t think they’ll be very worried by the prospect of a Kamala Harris presidency because they would see it as a lot of continuity from the Biden administration.”

Ms Harris has yet to officially win the Democratic nomination but she is the favourite and has been endorsed by other possible contenders, like Governor Gavin Newsom of California.

To ensure Australia’s interests are well served in the US, former Washington-based US ambassador Arthur Sinodinos has urged the government to respond carefully.

“It’s not about whether we like a particular candidate or a particular president – these relationships transcend countries, transcend personalities, they transcend parties,” he told ABC radio.

The prime minister described Ms Harris as a “good friend of Australia” while noting that the outcome of the Democratic convention in August is a matter for the US.

Mr Albanese sent Mr Biden his well wishes and paid tribute to his “extraordinary record”.

“President Biden deserves to be recognised for, once again, not putting himself forward first, but giving his first consideration to being what he believes is in the interests of the United States of America, as he has done his whole public life,” he told reporters in Cairns.

Australia’s ambassador to the US Kevin Rudd, whose prime ministership fell victim to a leadership spill in 2010, noted the difficulty of Mr Biden’s choice.

“Leadership can be a lonely place,” he posted on X.

“We can all take pause to recognise and respect the difficult decision President Joe Biden has made today.”

Opposition Leader Peter Dutton also thanked the US president and pointed to the security alliance between the US, UK and Australia as one of Mr Biden’s achievements.

“I thank the President for the support and abiding friendship he has shown to Australia,” he posted on X.