Despite the apparent "off the cuff" nature of Mr Trump's remarks during his campaign, it would be self-defeating not to see a significant consistency and continuity in his pronouncements on foreign policy. It is not difficult to define some key orientations in the way he looks at the role of the United States in the world. Many tenets of US foreign policy will be revisited should he make it to the White House next November.
First, there will be a definitive end to the attempts of the Obama administration to give a more multilateralist approach to US foreign policy - seen as a sign of weakness and disarray by the presumptive Republican nominee. There will also be an end to the notion which has dominated Washington's policy over the last 20 years that a key American objective is "to make the world safe for democracy". What Donald Trump is expressing through his "America first" slogan - and with a brutality unprecedented in modern US political history - is in fact the ever-latent isolationist strand of the American psyche. Add to that a solid dose of protectionism.
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Second, a Trump administration will put tremendous pressure on US allies in Europe and Asia to either contribute significantly more to the cost of US military efforts or to forget about US protection. Contrary to all US administrations, Mr Trump does not consider that by extending its military protection to Europe, Japan or South Korea the US is also serving its own strategic interests. This goes way beyond the recurring US complaints - so far with no impact - about most NATO allies not fulfilling their commitment to devote two per cent of their GDP on defence. In fact, the message is much blunter: "Be ready to spend much, much, more or you are on your own."
Third, despite - or even because of - the rhetoric about "making America strong again", a Trump presidency would not necessarily mean endless crises and rising tensions with Russia and China. Donald Trump loves "strong men" and, despite divergences with Moscow or Beijing, he would see himself at ease dealing with Vladimir Putin or Xi Jinping. In fact, while criticising the present administration for not dealing with Beijing from a position of strength, he has pledged to seek better relations with both Russia and China and has stayed far away from the Obama administration notion that Russia is now the "number one threat" to US national security. However, there is no indication so far on how the Russian and Chinese leaders would look at a Trump presidency.
Fourth, expect an even harsher approach from Washington in the fight against terrorism and ISIS if Donald Trump wins the White House. He has specifically mentioned destroying the captured oil fields bankrolling ISIS, and putting more pressure on Arab monarchies to step up their military and financial efforts. However, it remains to be seen how he would on the one hand threaten to leave European and Asian allies on their own, and on the other hand, ask them to act jointly with the US to improve the efficacy of the war against terrorism. The same applies to the Arab states.
This is such a departure from what has been expected from the US in recent decades - whether from a Republican or a Democratic administration - that many governments around the world are understandably scared of the prospect. This is aggravated by the fact that nobody can really fathom who around Mr Trump has a role or an influence in shaping his foreign policy orientation. It is even tougher to guess which foreign policy experts would join Mr Trump if he is elected, given his views are anathema to the Republican establishment which sees them as adverse to US long-term strategic interests.
Of course, a Trump victory next November is far from assured. When all is said and done, Hillary Clinton remains the favourite. And despite all the misgivings about her, she would provide a much steadier hand to US foreign policy, continuing to secure and assert America's role and place on the world scene in a predictable way. So apocalypse, or something close to it in the eyes of many around the world, is not necessary next November.
However, one nagging question remains: Given the strength of the populist wave pushing the Trump and Sanders campaigns, could a Hillary Clinton - especially if her margin is close - afford not to take into account some key messages that the US public has been sending since last fall? For instance, by reversing position on the Trans-Pacific Partnership agreement she has seemed to acknowledge its rage on trade issues. In the White House, would she just revert to the same policies that the presidential campaign has put into question? Candidates can say one thing during the campaign and do the opposite once in power. But is not this very kind of attitude from the establishment that has generated the wave propelling Mr Trump?
Twitter: @ClaudeSmadja