Terry Barnes is an Australian political writer and was a senior adviser to Tony Abbott in John Howard’s government.

Americans are rightly proud of living in the world’s greatest democracy. Citizenship of the one remaining superpower is a great privilege, and American chauvinism about their economic and military might often is well-founded.

But such global pre-eminence also carries great responsibilities. Electing a president who can competently double as de facto leader of the planet is one such responsibility.

Beyond the 220 million or so Americans eligible to vote in presidential elections (of whom less than 150 million actually are registered to vote), billions more around the world wish they could have a democratic say in choosing someone who, as President of the United States, will have profound influence over their lives.

Given the profound reach of America’s global leadership, they need someone in the Oval Office who understands the world outside the United States (indeed, knows that there is a world beyond the US); can be trusted to act sensibly in both foreign and domestic policy having global significance; and who inspires confidence in both the presidency and the United States herself.

They certainly want someone commanding great respect not just because of their awesome office, but because they are, as individuals, clearly worthy of it.

But presidential contests, especially in their early stages, are highly insular and parochial: what matters are Hamburg, Iowa and Manchester, New Hampshire, not their better-known namesakes.

With the 2016 race already off and running, over twenty Republicans and Democrats already are vying for nomination, with the Republican field so large that this month two debates in Cleveland, Ohio were needed to showcase them.

Outside the US, however, there are only two candidates who so far are widely known other than to politicos: Hillary Clinton for the Democrats and Donald Trump for the Republicans.

Clinton has been in public life for decades as First Lady; 2008 presidential front-runner who crashed and burned before the Obama juggernaut; US senator and most recently Secretary of State.

We may not always like or agree with Clinton, and her political and policy record is controversial and mixed – and overshadowed by her husband, Bill, as well.

We do more or less know, however, what we’d get with Hillary, and from an international perspective she is plausible in terms of her record, character and presentation.

Trump is well-known as a billionaire property tycoon, star of widely-syndicated reality television programme The Apprentice, and simply as a brash and arrogant man fond both of the limelight and his own opinion.

He generates strong feelings for and against, and his ferret-like hair much mirth, but as a presidential candidate and potential first statesman of the planet, Trump is a huge unknown.

His bombastic campaigning since he announced his candidacy first amused, then bemused and then, especially after last week’s first Republican candidates debate, frankly scares.

Candidate Trump may be standing as a Republican, but he is no respecter of conservative values, including courtesy and compassion.

He has denigrated an increasingly long list of respected American figures, now including former Republican presidential nominee John McCain, and Fox News presenter Megyn Kelly, who confronted him in Cleveland.

His is an aggressively populist, anti-immigration manifesto that wouldn’t have been out of place in America’s isolationist 1930s.

Trump’s message and conduct as current Republican frontrunner hardly are those of a putative head of state, raising serious questions of whether he is temperamentally suitable to the presidency and how he would perform on the international stage.

How, for example, would President Trump handle the subtleties and frustrations of international diplomacy, let alone decisions of peace and war affecting billions?  How would he deal with egos as large and unpredictable as his own, like Vladimir Putin’s?

When President Trump first meets David Cameron as a fellow leader, would he apologise for once having tweeted that Cameron is a “dummy”?  Would any foreign leader who dares challenges him be branded with favourite Trump epithets, loser or moron?

Worse, Trump invites the ridicule and contempt of those with whom he would deal if elected.

Following the first Republican debates, an Australian junior minister with a foreign policy background, Josh Frydenberg, very undiplomatically called him a “dropkick” on Australia’s equivalent of Question Time. Frydenberg only said what millions around the world, surely, are thinking.

In 2008, a BBC World Service poll covering 22 countries, including the UK and Australia, found support for then-Senator Barack Obama over John McCain ran much more strongly than it did in the United States. Should “The Donald” win the Republican nomination or, as he implies, stands even if he doesn’t, whoever is his Democratic opponent surely will have crushing support in any similar international poll.

But having no vote, international opinions don’t count.

If conventional political wisdom applies, Trump’s presidential candidacy should crash and burn well before the 2016 Republican National Convention in Cleveland, Ohio.

But with Hillary Clinton under pressure over her campaigning performance, her business interests, and her private emails and record as Secretary of State, and given his firming Republican frontrunner status, the disruptor Trump actually could win his nominal party’s nomination, and perhaps even the presidency itself.

Americans’ choice of president is a matter of global, not just national, significance. Our American friends may not recognise it, and presidential campaigns don’t care about it, but they do owe it to the rest of us to make a wise choice.

This means having the wisdom not to not indulge Trump’s grandiose presidential ambitions.

In his famous inaugural address, John F. Kennedy asked his “fellow citizens of the world” to “ask not what America can do for you”. When it comes to assessing the claims of the many candidates and choosing the next US President, however, their fellow citizens of the world should ask Americans, whether Republican or Democrat, to vote as if the world depends on it. Will they?