Malcolm Turnbull's trip to Washington has been newsworthy precisely because it has been so un-newsworthy.

Which is simply to say that given Trump's penchant for unpredictable speech and behaviour, the fact that the meeting between these two leaders went off without a hitch seems like an accomplishment in its own right.

With previous US administrations this would not even have been a question due to the resilience and importance of the broad and deep relationship between the two nations.

However, with an American president whose foreign policy can be difficult to discern and whose moods are erratic, this has not been a given and will continue to be a challenge for officials in Canberra.

More important, and less often discussed however, are the broader implications of dealing with such unpredictability.

Trump's uncertain foreign policy

While some see more continuity than change in Trump's foreign policy, the majority of outside observers have found it challenging to understand the intent of White House policy on most key issues from NAFTA and NATO, to Asia and the Middle East. To some degree, there will always be uncertainty after a US presidential election about how much US policy will change.

This uncertainty is heightened when there is a transition from one party to another. It is heightened further when the president makes statements which are outside the bounds of normal foreign policy discourse and procedurally opaque.

Trump, to be sure, wants to be less predictable than his predecessors and international opponents, declaring "we must, as a nation, be more unpredictable".

Trump, to be sure, wants to be less predictable than his predecessors and international opponents, declaring "we must, as a nation, be more unpredictable".

There are countervailing forces in the current US administration. Secretary Mattis, National Security Advisor H.R. McMaster and Secretary of State Rex Tillerson are colloquially referred to as "the adults in the room" and have attempted to give structure, organisation and coherence to the administration's foreign policy. But the President's unpredictability continues to undermine such efforts, as his pronouncements on issues ranging from trade to North Korea have repeatedly and explicitly undercut his cabinet secretaries.

The result has made it nearly impossible to understand what is a tweet and what, ultimately, is policy.

Unpredictability gives Trump leverage

As Trump knows, from a negotiating perspective, and certainly when dealing with competitors, unpredictability carries some advantages and, judiciously applied, can even provide leverage.

Take North Korea. While impossible to know what is going through the mind of Kim Jong-Un, there can be little doubt that he now has less clarity about which of his actions would trigger a devastating military response. This lack of clarity has the potential to inject a degree of caution into his plans.

Furthermore, fear of what Trump might do also has some utility in getting both China and Russia to implement more rigorous sanctions against Pyongyang.

But elevating unpredictability to a strategy has downsides as well. It has confused allies, promoted instability in critical trade relationships, elevated the risks of miscommunication in a crisis, and left the world questioning the credibility of American commitments.

The actions required to demonstrate resolve and to signal deterrence have likely increased, as have the chances of unintentional escalation.

The actions required to demonstrate resolve and to signal deterrence have likely increased, as have the chances of unintentional escalation.

Some of this will be offset by the words of key US cabinet members and the might of the American military, but no matter how many times US alliances are reaffirmed by senior officials, as President Harry Truman said, the buck stops with the president. Presidential unpredictability, therefore, raises fears that America will not live up to its security guarantees.

As an official from a major US ally in Asia commented, "Washington, D.C. is now the epicentre of instability in the world".

More significantly, if the United States continues to behave erratically on the international stage, it could become a threat to the international order itself as perceptions of US steadiness have traditionally backstopped that order.

Credibility is of course impossible to measure. But its loss matters enormously for both friend and foe.

Australia can help

Given the near certainty that Trump will continue acting erratically, and the magnitude of the stakes, broad Australian support for, and engagement with America is crucial.

Given the near certainty that Trump will continue acting erratically, and the magnitude of the stakes, broad Australian support for, and engagement with America is crucial.

In this regard, Canberra's reminders of the ties that Australia and America share in investment, security, and democratic values, will provide dividends for both countries.

Partially, this should be done to educate American policymakers about Australian concerns in the Asia-Pacific region, and partially this should be done to reinforce shared values.

In these unusual times, foreign leaders, particularly close allies, have a unique opportunity to amplify key messages.

Otherwise, the field will be ceded to those pushing a message of American withdrawal and foreign actors with less benign intentions.

If there is concern that the White House has stepped back from its role as guarantor of the post-war order, and if allied nations believe that this order, for all its flaws, is still in their interests, they must step up to the defence of it — to Washington and to others.

Read Charles Edel's new report on the history, the powers and the limits of the presidential office.