Washington | Donald Trump views the US-Australia alliance as a "special relationship", the Republican presidential candidate's top advisers told ambassador Joe Hockey.
The reassurance came only days before Mr Trump sent Asian allies into a worried frenzy this week, by publicly flagging the likely shrinkage of the American military footprint in Asia and forcing Japan and South Korea to pay billions more for US protection, if he becomes president.
Foreign policy experts warned the retreat of American leadership in the region could create a gap for an emboldened China and unpredictable North Korea to be more militarily provocative. 
Similarly, his unorthodox non-interventionist style and desire for the US to pull back from the North Atlantic Treaty Organisation may encourage Russia to be more aggressive in Ukraine and elsewhere.
In Washington, foreign diplomats from various embassies are growing increasingly worried about Mr Trump's isolationism and anti-free trade populism, as well as his attacks on foreign leaders.
Mr Trump has labelled Angela Merkel's leadership of Germany a "disaster", ridiculed Mexico for not stopping illegal immigrants crossing into the US and drawn scorn from British Prime Minister David Cameron for a call to ban Muslims entering the US.
Foreign diplomats say they have had difficulty establishing dialogue with Mr Trump's campaign, let alone the presidential candidate himself.
Mr Hockey is believed to be one of the few, possibly the first, foreign ambassador to secure a meeting with Mr Trump's team.
The former treasurer met senior Trump campaign advisers in Washington DC last week. They are understood to have discussed defence, trade and economic ties between the two close allies.
A person familiar with the conversation told AFR Weekend Mr Trump's aides told Mr Hockey the US had a special relationship with Australia.
Australia and the US last year celebrated the 75th anniversary of diplomatic relations and have fought together in every significant conflict since World War I. The US, in effect, guarantees Australia's security through the Australia, New Zealand, United States Security (ANZUS) treaty.
Mr Trump, a billionaire property developer and marketing king, has cut business deals in Australia.
Democrat frontrunner Hillary Clinton, the favourite to win the election, is assembling a top Asia advisory team, Hillary for America Asia Policy Working Group. It is led by former senior diplomat Kurt Campbell, who is well known in Australian political circles and is an acquaintance of Prime Minister Malcolm Turnbull.
Despite Team Trump's assurance to Australia, defence hawks said even if he maintained existing US military resources in Australia, it would count for little if other forces withdrew from neighbouring areas.
"His logic is still that America has little strategic interest in being in Asia so that would worry me and should worry Americans as well," said John Lee, a defence and Asia scholar at Australian National University.
The US has about 1200 marines stationed in Darwin. The number is due to gradually rise to 2500, as part of President Barack Obama's "rebalance" to Asia. The US also has significant intelligence and other military assets in Australia.
Spanning the recent Gillard-Rudd and Turnbull-Abbott governments, there has been niggling disagreement with the Obama administration over cost sharing for new facilities for extra marines and a bigger runway and refuelling facilities for US bombers.
If Mr Trump is elected president, the financial tensions could heighten because the Republican frontrunner has made it clear he believes America is contributing too much for deployments in Asia and Europe.
The business tycoon wants to prioritise fixing things at home, by cutting the federal government's $US19 trillion debt, investing in dilapidated infrastructure and creating better-paying blue collar jobs by reviving the manufacturing sector.
Americans have grown wary of being entangled in foreign wars such as Iraq and Afghanistan, given the trillions of dollars in costs and thousands of US lives lost.
A Pew Research Center poll found a record 52 per cent of Americans agreed in 2013 that the US "should mind its own business internationally" and let other countries get along as best they can, compared with 41 per cent who said so in 1995 and 20 per cent in 1964.
The Australian ambassador, who took over from Kim Beazley in   January, will attempt to meet Mr Trump and other presidential candidates during the campaign.
It is unclear if Mr Hockey directly raised concerns about Mr Trump's lashing of free trade deals and opposition to the 12-country Trans-Pacific Partnership, a deal that is yet to be ratified by the US Congress.
The TPP is opposed by other presidential candidates Bernie Sanders, Ted Cruz and Mrs Clinton, because of claims that trade agreements have wiped out manufacturing jobs and don't adequately deal with currency "manipulation".
Trade Minister Steven Ciobo took the unusual step last month of criticising Mrs Clinton for opposing the TPP she previously supported as secretary of state, saying her disapproval was based on union misinformation.
The Turnbull government is worried about anti-free trade rhetoric in the presidential campaign. Mr Turnbull personally lobbied congress members in   January to pass the deal. In Washington, Mr Turnbull spoke via telephone to Mrs Clinton and Republican contender Marco Rubio, who has quit the presidential race.
The Coalition pledged to increase defence spending by nearly $30 billion over the next decade and plans to restore outlays to 2 per cent of GDP. The US was upset Canberra's defence spending fell to 1.6 per cent under Labor, the lowest since before WW II.