Australia has structured its entire national defence around the concept of a reliable US alliance. So what does it do when an incoming US president says he's prepared to walk away from America's alliances?
Donald Trump is much more than a celebrity demagogue. He's a threat, as Japan's former defence minister Yuriko Koike has said, to "global stability, and even peace".
A leading US adviser to the Republican party on foreign policy, Mike Green, says: "Donald Trump is an equal-opportunity insulter to all our friends and allies.
"He hasn't said anything positive about any country except Russia because he likes Vladimir Putin, and he's attacked all our big allies – Japan, Korea, Britain, Angela Merkel," the chancellor of Germany.
He has said he's prepared to abandon all of the US's principal allies, including the bedrock of America's relationship with Europe, the NATO alliance, unless they pay more money for their own defence.
"He portrays all this like a real estate deal – if you don't get the price you want, you just walk away from the deal," Green tells me. And as Trump himself has said: "You can never be too greedy."
Trump is not the incoming president, but now that he's going to be the Republican candidate he has a very realistic prospect of getting there. And he has not criticised Australia. But if he's prepared to dump much bigger and more central US allies such as Japan or Britain, why wouldn't he shrug off a more peripheral one like Australia? Japan's Koike last month called Trump's remarks "the height of irresponsibility". Yet she said that the world needed to emerge from a state of denial: "It may be time to admit that America really could return to the 'America First' isolationism of the 1930s, which Trump has just proclaimed as his goal."
Officials and experts like to rationalise that, even if he manages to defeat Hillary Clinton, Trump won't carry his campaign rhetoric into office. Mike Green, who was responsible for Asia policy in the George W. Bush White House and was an adviser to the candidacy of Jeb Bush, says that there are a couple of reasons to think that president Trump would not be the same man as candidate Trump.
One is that Trump's positions are too confused and contradictory to be implementable. In the words of an open letter signed by more than 60 Republican foreign policy experts, his statements are "wildly inconsistent and unmoored in principle".
Another is that, as president, Trump would discover the limits to his power. Any attempt to cut allies adrift would be opposed by the Pentagon, the State Department and by his own Republican caucus in the US Senate. Says Green: "It would be an all-consuming fight."
Yet Green nonetheless concedes the possibility that Trump could indeed vandalise the network of US alliances painstakingly built and sustained over 70 years.
"You can picture a scenario where Trump goes to Australia and says: 'Australia is just free riding on us and just sending small numbers [of forces] compared to ours. I love Australia, it's a huge country, I love Fosters, but I'm pulling out of the Darwin deal for rotating deployments of US Marines and I want to renegotiate the ANZUS treaty.'
"That's a scenario I could easily imagine."
The conservative US Republican commentator and adviser Ying Ma last week spoke at a round table at the US Studies Centre at the University of Sydney.
She was a media aide and policy adviser to the candidacy of Ben Carson, who pulled out of the Republican race last month and then endorsed Trump. Carson and Trump have many links; Ma is tipped as a possible part of the Trump communications team. Certainly, she was projecting Trump through a benign lens in Sydney last week.
I asked her whether US defence allies should assume that existing US commitments would remain intact under a Trump administration, or whether they should start hedging their bets?
"Yeah, I guess they should hedge a little bit," she replied. "I don't think a shake up of our alliances would be that bad."
With a rogue Russia, an increasingly assertive China and a virulent global terrorism movement, among other security problems, it's an unnerving moment for US allies to have to confront this possibility.
Ma's advice to America's allies was to make contact with the Trump campaign and seek to explain the importance of the alliances. Many US allies "have made a huge mistake and not reached out to Trump" she says.
Joe Hockey hasn't made that mistake. Trump advisers reportedly have offered some reassuring words to the Australian ambassador.
But the head of the Australian Strategic Policy Institute and former chief strategist for the defence department, Peter Jennings, says that Trump is part of a bigger phenomenon that Australia should be thinking about.
"There's an emerging isolationism in the Republican party that is a concern," Jennings tells me. "It's worth thinking about it – what do we do if we are in fact facing an inward-looking US that doesn't want to take an interest in Asia-Pacific security?"
What does the deputy sheriff do if the sheriff hands in his badge and retires to the ranch?
"We'd have to think further about how to get closer to Japan, redouble our efforts with Indonesia and other parts of the network of relationships that we have," Jennings advises. "For us, a world without the US alliance would be much more difficult and expensive. We have the sovereign capability to bolt submarines together, for example, but for 90 per cent of the weapons systems and sensors there's a trail back to the US. Some of our frontline capability would completely go."
Australia wouldn't be capable of developing its own stealth aircraft industry, for instance. "For some other things we might be able to manage for ourselves but not with 2per cent of GDP", the current plan for Australia's defence budget.
"It'd be something north of that, and still leave us with diminished capability. It's where our strategic circumstances would force us to go."
These are the questions that Australia has to confront, however discomfiting. In Trump's view of geopolitics as a real estate deal, is Australia prepared to stake its security on his valuation?
Peter Hartcher is international editor. sydneymorningherald Illustration: John Shakespeare