Last week Prime Minister Turnbull committed Australia to join the United States in a war with North Korea. His remarks were strangely brief and informal for such a weighty issue, and left it rather unclear under what circumstances he would be willing to fulfil that commitment. Much of the language he used—phrases like ‘shoulder to shoulder’ ^[1] and ‘joined at the hip’—seemed to suggest that the specific circumstances of conflict were irrelevant: we would fight alongside America however the war had come about, come what may.

Turnbull did use the words ‘if there is an attack on the United States’ ^[2], which may have been intended to limit the commitment to supporting America in responding in self-defence to a clear act of aggression by North Korea. If so, he would have been well advised to make that clearer, because in the current context that’s far from the most likely scenario in which America would seek Australia’s military support against Pyongyang.

Despite Kim Jong-un’s bellicose talk, a serious direct attack on America or its allies has always been very unlikely, because the North Koreans know that it would lead to a devastating war that would destroy their country. And the Americans understand that perfectly well. Their real concern is the North’s rapid progress towards developing an ICBM. And while the temperature may have gone down a little in recent days after last week’s heated rhetoric, that problem hasn’t gone away.

No one seriously believes that diplomacy and sanctions will fix things. So over the next few months, the North Koreans will probably stage further tests offering clear evidence of progress towards an operational ICBM force. Would the US then launch a war—and it would be a very big war indeed—to stop them? It’s far from clear where Washington stands on that at present. Much of the tough talk about military options being on the table is intended to scare Pyongyang, but how would the Americans jump if their bluff was called?

The messages from the administration on that are mixed. Key figures like secretaries Mattis and Tillerson seemingly swing between caution and belligerence, while many others in Washington plainly believe that a major war is better than a North Korean ICBM.

And obviously, after all that’s been said, doing nothing would be a humiliating backdown, and a big blow to President Trump’s ego and America’s credibility. So it’s really quite possible that a war with North Korea will be initiated by the White House in the next few months.

One hopes that Turnbull has thought carefully about whether his commitment to stand shoulder to shoulder with America would still hold if that happens. It would be a much tougher call than supporting America if it was fighting in self-defence against clear aggression. It would require him to do more than simply invoke the alliance as ‘the absolute bedrock of Australia’s security’.

He would have to weigh the real strategic questions involved, and there are no simple answers. It’s not enough to say that North Korea’s nuclear and missile forces are a threat to regional security: one has to decide whether that threat is bad enough to justify what it would cost to remove it.

These are very hard choices between very unpalatable alternatives, but they must be faced realistically. The direct threat posed to the US itself is less than it appears at first sight, because America is so well placed to deter a North Korean nuclear attack on the US. There is always a theoretical chance that deterrence might fail in some way, but no leader in Pyongyang could be in any doubt that an attack on a US city would result in the total destruction of North Korea. That means the risk of such an attack being mounted by a rational leader is very low indeed.

That leaves the risk of an irrational action, or an accidental launch. Neither of those can be completely ruled out. Accidents are always possible, especially as one might imagine North Korea’s command and control systems leave a little to be desired. An act of sheer irrationality is also clearly credible, either by the North Korean leadership or by a subordinate in the chain of command.

This risk is not new or unique to North Korea. For decades America has lived with the threat of nuclear attack from a number of nuclear powers as a result of deterrence failure, accident or irrationality, and so have many other nations. Adding North Korea to the list of countries that could hit the US with nuclear weapons increases the risk somewhat, but doesn’t change its nature fundamentally. And it’s hard to argue that America would be justified in launching a war costing hundreds of thousands of lives to eliminate that risk, or that Australia would be justified in supporting it.

But that is not the only consequence of a North Korean ICBM. I have argued elsewhere ^[3] that the more significant effect would be to weaken America’s alliances in Asia by undermining the credibility of US extended nuclear deterrence undertakings. But it hardly makes sense to fight a major war to try to avoid that. And Trump’s suggestion that he would do so only adds to the broader damage to US strategic credibility in Asia and beyond caused by the president’s tendency to issue threats that he can’t realistically fulfil.

Turnbull should both think and speak very carefully before further committing himself and Australia to support US policies that seem certain—however things play out—to do a lot of damage to America’s strategic position in Asia, and hence to Australia’s real interests.