Standing on Washington’s Mall in January, 2009 on an ice-cold day, observing the 44th president of the United States of America being sworn into office by the Chief Justice of the Supreme Court, much seemed possible.

We had arrived – so it seemed – at a moment of hope and change, or, as the historians put it, a hinge point in America’s continuing search for a perfect union.

Destiny had descended upon us.

Here was America’s first black president assuming office after the bleak days of George W Bush, who had bet his administration on a botched war in Iraq to get rid of non-existent weapons of mass destruction.

Five years after the invasion of Iraq, and in the midst of a global financial crisis, America was to have a new beginning with a new administration and a new president. All of this would be a salve to the country’s wounds and enable it to move on.

Eight years, or two presidential terms, after that day in 2009, America has arrived at a new “hinge point”. This time, the message being delivered by the latest resident of Pennsylvanian Avenue is less one of hope and change than that of America first and foremost.

No-one can predict how a Trump administration will evolve beyond the near certainty the world – and America in particular – is in for a bumpy ride, and possibly a disruptive one.

Trump supporters would say that disruption is what is needed after years of drift in which the president’s diffidence in the exercise of power contributed to a global vacuum filled by bad actors. This is notwithstanding that the right seemingly cannot make up its mind whether Russia’s Vladimir Putin is good or bad, or simply misunderstood.

What is needed, according to a consensus view on the right, is a reassertion of American power, leaving aside their candidate’s isolationist rhetoric on the campaign trail.

How this circle – between Trump’s isolationism and the assertiveness of his supporters – will be squared will be not the least of the consequential questions to be addressed in the months ahead.

Can America be both isolationist and great again? I doubt it.

In all of this, views on the Obama legacy, like the expectations of a Trump presidency, are all over the place. This reflects the uncertain times in which we live.

So, what is the fair judgement of the Obama presidency, and what might reasonable expectations be of Trump’s tenure?

First, Obama.

In Australia, a narrative has evolved that holds the outgoing president guilty of sins of omission and commission. His unwillingness to twist former Iraqi president Nouri al-Maliki’s arm and enable US troops to remain in Iraq after 2011 has contributed to the further unravelling of that country and the rise of IS.

According to this view, Mosul would not have fallen to IS if American forces had remained, and the spread of the caliphate would have been curtailed.

Left unanswered by the critics is to what extent America would have needed to re-engage to forestall the encroachment of IS from its strongholds in Syria across a porous frontier into Iraq.

Such criticism of Obama’s diffidence in Iraq would have more credibility if it was not evinced by those who displayed exceptionally poor judgement in their advocacy of the Iraq invasion in the first place.

In the case of Syria, critics are on firmer ground. Having drawn red lines around the use of chemical weapons by Syria’s Bashar al-Assad against his own people, Obama’s reticence in taking reprisals will almost certainly come to be regarded as a mistake.

By standing back, the administration allowed a vacuum to evolve and be exploited by Russia and Iran, among others. This is not to mention all the other consequences of an enormously disruptive civil war, whose fallout has spread beyond Syria’s borders to its immediate neighbourhood and into Europe.

Obama argues that a US response to Syria’s misbehaviour enabled agreement with the Russians to quarantine Assad’s chemical weapons. But this avoids bigger questions about what might have transpired if America had pursued a more assertive role, including establishment of a no-fly zone over northern Syria and safe havens for the displaced.

In fairness to Obama, he had staked his presidency on winding back America’s debilitating commitments on the ground in the Middle East, believing they were counterproductive. In that regard he has a point.

In the view of Australian critics, Obama’s “pivot” to Asia has yielded disappointing results, but he should be given credit for seeking to rebalance America’s strategic interests away from costly commitments in the Middle East, even if he might have pursued this goal with more vigour.

His efforts to promote a regional trading partnership should be noted.

On other contentious issues such as the Middle East peace process, Obama rates barely a pass. While it is true that circumstances on the ground could hardly be less auspicious, he could have done more to exert pressure on both the Israelis and Palestinians, and earlier.

Now, Trump:

In Australia, the new president’s arrival in the White House is being viewed with a mixture of alarm and expectation. Hawkish elements are looking forward to a more assertive approach towards China’s regional ambitions, while concerns are harboured inside and outside government about disruptions to a regional trading environment on which Australia relies.

No Australian government wants to find itself in a position where it is obliged to make a choice between its history - in the form of its alliance obligations - and its geography in a China-looming Asia-Pacific.

What we are seeing domestically is an overdue debate about the need for greater self-reliance in a new era in which American power may be receding, or at best no longer unchallenged.

Trump’s ascendancy is hastening this process.

Finally, the perennial question among historians and others as to how the Obama presidency will be judged historically, and whether in time he will be seen to having found his way into the ranks of better presidents.

On the basis of his having steadied the ship on assuming office during a financial crisis presided over by his predecessor, and restoring his country’s economic well-being in what has been a long slow recovery, he deserves more credit that is being accorded. History will judge him better than his critics anticipate.