Illustration: John Shakespeare Beijing would have asserted de facto control of the world's most valuable commercial artery and 3.6 million square kilometres of ocean. The other six countries with claims to parts of the South China Sea would have been sidelined. Other countries would be permitted to use it only with China's consent. "The question is, what are we going to do about it?" posed the director of the Australian Strategic Policy Institute, Peter Jennings, a former head of strategy for the Defence Department. His comments were made to a closed-door session of the Australian American Leadership Dialogue but later repeated to me for publication on the record. Executive Director of Australian Strategic Policy Institute Peter Jennings. Credit:Jay Cronan The question was an uncomfortable one for many in the audience, which included senior officials, politicians and others from both countries. Because, as Jennings spoke, the US President was abusing the leaders of America's best allies in Europe. And preparing to sit down and make nice with the leader of its greatest traditional rival, Russia.

Australian and American representatives I spoke to, Labor and Liberal, Republican and Democrat, officials and academic experts, agreed that the Jennings scenario was plausible; some said it was likely. None thought it implausible. What would Donald Trump do? Would Trump's America be steadfast in a crisis? Or would the administration be too distracted, too confused, or too compromised by its other negotiations with China to stand its ground? Five hundred years after Portugal's Vasco da Gama first took Europe into the Indo-Pacific, are we in the final weeks and months of the era of Western dominance? Loading "It's right to expect some kind of testing by China to see how far they can go, to find the limits. You have to be unwaveringly consistent and firm," says Michele Flournoy, a former top Pentagon policy adviser under both Barack Obama and George W. Bush.

"China's pattern of behaviour is like they're boiling a frog - keep the temperature high enough to change the frog from live to one you can eat, but not with any extreme changes so that the frog jumps out of the pot," she tells me. "I don't think China is interested in a war with the US. They're trying to change the status quo, with each action calibrated to a level below the level required to provoke action from the US," says Flournoy, also a participant in the Australian-American Leadership Dialogue. America did act once. When China unilaterally declared a restricted aviation zone above contested waters in the East China Sea in 2013, Washington challenged it. And Beijing backed off. An airstrip, structures and buildings on China's artificial Subi Reef in the Spratly chain of islands in the South China Sea. Credit:AP The US flew a pair of B-52 heavy bombers through the zone and China made no effort to interfere. "We were very successful under Obama," on that occasion says Flournoy, who now runs strategic advisory firm WestExec. "We said we wouldn't respect it and they decided it wasn't worth the risk."

But on other critical occasions under Obama, America failed to act. Obama told China to stop building islands in the disputed areas of the South China Sea. Beijing simply ignored him. Obama did nothing. While the US has dithered, China's President Xi Jinping has been clear and purposeful.

"Like clockwork," says Jennings, "every three to four months they take another step to consolidate their gains in the South China Sea", where Beijing has constructed man-made islands in contested waters and equipped them with runways, reinforced hangars, and batteries of anti-ship and anti-air missiles. A Chinese heavy bomber recently touched down on one of the islands for the first time. What's going to be the position of America's new President in the face of this steady expansion? Would Trump stand up for the international freedom of navigation? Or would he cut a deal with Xi and leave the other countries of the region - including US allies Australia and Japan - to fend for themselves? US President Donald Trump gestures while speaking to NATO Secretary General Jens Stoltenberg Credit:AP If Trump's behaviour in Europe this week is any guide, allies shouldn't expect much consideration from him. He'd earlier declared that the great treaty holding the West together, America's NATO alliance with Europe, was "obsolete".

This week he tweeted that NATO's European members were not only failing to pay their share of the alliance's defence spending, they were also running trade surpluses with America. His punchline: "NO!" He's right that most of the Europeans have been free-riding on America. That's why all the European governments in NATO grudgingly agreed years ago to raise their defence spending to at least the equivalent of 2 per cent of GDP by 2024. Only eight of the 29 NATO members meet this benchmark today. The US spent the equivalent of 3.1 per cent of GDP last year according to the Stockholm International Peace Research Institute. Europe's economic giant, Germany, is a military pygmy, spending 1.2 per cent last year, according to the institute. Australia, for comparison, spent 2 per cent of GDP equivalent. Loading But while Trump might be right to gripe and just in his cause, he is ugly and abusive in his tactics. By insulting European leaders, Trump makes it impossible for them to get the popular support they'd need for big increases in military outlays, argues the prominent commentator Robert Kagan, a scholar at the Brookings Institution. "The democratic alliance that has been the bedrock of the American-led liberal world order is unravelling," Kagan writes in The Washington Post. "Despite our human desire to hope for the best, things will not be okay. The world crisis is upon us."

Is this right? Is Trump deliberately making impossible demands on NATO? Is he trying to smash an alliance created to defend Europe against Russia in order to gratify his Russian alter ego, Vladimir Putin? Or is it a negotiating tactic to jolt the Europeans into action? Steve Bannon, once Trump's chief strategist, no longer speaks for the President but he does interpret him: "He's trying to make the alliance work. He's trying to have a partners' conversation," he tells me. "The President's central point is this - America is not an imperial power, and we don't want protectorates. We want allies. This is just as true for Australia. We are looking for allies. Steve Bannon is no longer Trump's strategic adviser but he does interpret his agenda. Credit:Bloomberg "Trump has his own style; he's not diplomatic. He's going to break some flatware. He talks bluntly and that's one of his sources of power with the American people. Here is the Trump doctrine - he's not going to go along with managed decline. NATO is in decline and everybody knows it."

The domestic politics of this? Bannon again: "We underwrite the security of the whole place," says Bannon, "and it's all on the shoulders of the 'deplorables'", a Hillary Clinton term that she used in an unguarded moment to describe Trump supporters. "It's the sons and daughters of the 'deplorables' who are in the US bases in Germany and Korea, on the US Navy ships in the South China Sea, and fighting in the Hindu Kush." So angrily demanding that pampered Europeans pay more for their defence is a popular point with Trump's voter base. And what will Trump do in confronting China? "He understands that the central geopolitical issue of the century is China versus the West," says Bannon. "He will not let the South China Sea go uncontested. He's been consistent on China for 30 years. He understands China is the main event. He's not going to back off." US Defence Secretary Jim Mattis. Credit:AP He says that the US Navy already is patrolling more actively and consistently in the South China Sea under Trump's defence secretary, Jim Mattis, and all reports suggest that this is true.

A longstanding friend of Australia's in Washington, Richard Armitage has served as a top US defence official and diplomat. He's a lifelong Republican who nonetheless refused to vote for Trump and cast his ballot for Hillary Clinton. He doesn't have much confidence in Trump, but nor does he think that the President is about to discard Australia as an ally. His advice: "For a change, the ally Australia will have to, at least temporarily, take the lead on issues. Take the lead on discussions and on planning against contingencies. Allies expect us to come forward; that's not going to happen under the present management." If China presses its case and the US fails to act, does the Royal Australian Navy have the option of trying to crash through any new Chinese exclusion zone? Australian and American experts were unanimous on this, best summed up by a former US official: "Try that without us, you're screwed." Loading Australia confronts two possible futures. In one, Trump's America demands the robust help of strong allies to resist Chinese ambitions. In the other, a fickle Trump proves unreliable, leaving Australia to navigate a lonelier existence in a Chinese-dominated sphere.

Either way, Australia needs to be more active, more robust and more assertive than it has ever been. It has the advantage that its main political parties are so far united in confronting the dawning reality of frontline responsibility. If Jennings is right, there's no time to waste. Peter Hartcher is political editor.