Let's put Mr Turnbull's diplomacy last week into context. While he was in China, US Defense Secretary Ashton Carter was in the Philippines talking up America's commitment to support Manila militarily against Beijing. At the same time, a senior Chinese general toured Beijing's bases in the Spraltys.
Meanwhile, the Permanent Court of Arbitration's judgement in the Philippines case against China is only a few weeks way, and credible reports say that China is preparing to build a base on the Philippine-claimed Scarborough Shoals or declare an air-defence identification zone over the Spratlys.
This all suggests that things are heading for some kind of showdown over the next couple of months. It seems the Court will find against China. If they do, China will probably react with some further provocation. And if that happens, Washington faces an ever-starker choice between responding militarily or taking a big blow to its strategic credibility in Asia. And so, in Churchill's plangent phrase, 'The terrible "ifs" accumulate'.
We cannot know whether or not these 'if's' will lead to a war, but we do know that this is just how wars often start: not when both states want to fight, but when each assumes it can get what it wants without fighting because the other will back down. Such a war, if it happened, would pose the gravest threat to Australia's security and prosperity in generations. And if war is only avoided by America backing down — which is becoming increasingly likely — then we face an almost equally grave collapse of the US role in Asia on which all our strategic expectations and policies are based.
This should be clear to Mr Turnbull and his advisers. If it is not, what further warnings of impending conflict are they waiting for before they take the risk of US-China conflict seriously enough to try to do something to avert it?
Which brings us back to Mr Turnbull in China last week. He didn't go to China to talk about this danger. He wanted to talk trade and innovation, but a well-timed warning in the Chinese media (interesting in itself) ensured that the main focus of his visit was on the South China Sea question and what he would say about it.
And what did he say? It seems he told the Chinese that they should stop building bases and deploying forces in the South China Sea, and instead submit their claims to adjudication in accordance with the so called 'rules-based global order'. To do otherwise, he apparently said, was contrary to China's own interests.
And what precisely was this expected to achieve? Did Mr Turnbull really expect that his remarks would apply that last bit of pressure needed to persuade China to abandon its newly-built bases, withdraw its forces, repudiate the nine-dash line and submit its claims over contested features to arbitration? That seems a long shot, to put it mildly. After all, the argument he put to them is one they have heard many times before, and it is hardly a zinger.
In fact the claim that China's actions are counterproductive to its own aims is almost certainly false. It assumes that Beijing wants to make friends and uphold the 'rules based global order', whereas their aims are clearly to display their growing power and replace the current order with 'a new model of great power relations'. In terms of furthering these aims, their pushiness in the South China Sea is working just fine.
So turning up in Beijing simply to rehearse well-worn clichés about regional order was not serious diplomacy. The natural conclusion is that Mr Turnbull neither intended nor expected his talking points to make any actual difference to China's policy, or to the situation in the South China Sea. He was just going through the motions, while the risk of conflict grows.
That seems close to a dereliction of duty, when the stakes for Australia are so high. But he got away with it politically because no one expected him to do anything more. Commentators assessed his diplomacy on the South China Sea solely as a test of his diplomatic mettle: would he show strength by speaking his mind, or chicken out and soften his message? No one asked what real difference it would make whether he did or not.
This prompts a question: why do our leaders aim so low in foreign policy, and why do the rest of us not expect them to aim higher? Why do we accept that the only thing at stake in Beijing last week was Mr Turnbull's reputation as a person willing to speak his mind?
Perhaps the answer is that we have lost the habit of serious foreign policy. For a long time we have been one of those lucky counties for whom the world works well to keep them secure and prosperous. Such countries easily take their good fortune for granted, and start to see diplomacy as a ritual in which one simply expresses one's views, and points are awarded merely for doing so. They forget that diplomacy can sometimes be an earnest and even desperate struggle to avoid disaster. What we saw in Beijing was classic lucky-country diplomacy.
It is reasonable to ask what Mr Turnbull should have done instead. That's a big subject for another time, but the first steps must be to acknowledge the nature and scale of the problem. That is not something he could start to do in Beijing. First he has to talk seriously at home about the risks and the choices that Australia faces, and talk seriously to Washington about their approach to China.
He could have done so in his Lowy Lecture last month, if he'd said something like what I've suggested here. But he ducked it. Perhaps he thinks there will be another chance later. He shouldn't bet on that because events are moving fast.
Photo by Lintao Zhang/Getty Images