Mr Donald Trump remains very unlikely to be elected president of the United States. But Mrs Hillary Clinton inspires neither adulation nor trust, and a Trump victory on Nov 8 can't be ruled out. That's why it's worth considering the sorts of risks that a Trump presidency would create - for Americans and the world. The biggest problems do not involve US relations with Russia or Iran - or even China, its primary geopolitical competitor. Instead, there are four other areas where Mr Trump is likely to create significant trouble.
First, there is the unexpected crisis. US presidential candidates spend 18 months trying to persuade voters that their plans are best. Yet, history shows that events far beyond a president's direct control create crises that must be faced. President Barack Obama inherited a global financial meltdown. Mr George W. Bush was blindsided by the Sept 11 terrorist attacks. Crucial to any president's legacy is effective management of entirely unexpected challenges.
Mr Trump's inexperience - he would be the first US president never to have served in either government or the military - his erratic temperament, and thin skin suggest he's less equipped than any presidential candidate in recent memory to handle a surprise emergency. In fact, his tendency to overreact to any perceived personal insult suggests he might even make bad situations much worse. In particular, his assertion that US sailors should respond to rude hand gestures from Iranians by "blowing them out of the water" tells a story we should take seriously.
Second, Mr Trump would badly damage US relations with key allies. Public antipathy toward him inside allied countries will make it harder for election-conscious leaders to support US action. In particular, Mr Trump's charge that the North Atlantic Treaty Organisation (Nato) partners aren't paying their fair share of Nato's costs will damage ties with European governments and voters. Threats to impose tariffs on Mexico and Japan will antagonise those countries, and a promise to eject 11 million undocumented workers from the US and build a border wall will antagonise millions of Latin Americans, even if he doesn't follow through.
His "suggestion" that Muslims from countries with a history of terrorism should be banned from entering the US will provoke Muslims everywhere and their governments. And Mr Trump's refusal to make clear which traditional commitments he'll honour and which he won't will strip allied governments of the domestic support they need if they are to accept more of the costs and risks that come with greater responsibility for their own security.
Third, all politicians divide the world into friends and enemies. Mr Trump is an extreme case, and we shouldn't be surprised if he goes further than most elected leaders to reward the former and punish the latter. This applies not just to foreign governments and leaders but to companies, journalists, non-governmental organisations, and even private citizens. That's the sort of action we might expect from Mr Vladimir Putin, Mr Recep Erdogan, a Central Asian dictator, or Mr Richard Nixon.
Finally, a President Trump would make US citizens, symbols of US power, and the US itself the single most attractive target for Al-Qaeda, the Islamic State in Iraq and Syria, and other militant groups. There is obviously nothing new about terrorist attacks, and would-be attacks, on American targets. The Clinton, Bush, and Obama administrations have all had to respond to terrorism.
Yet, Mr Trump's uniquely intense anti-Muslim rhetoric will encourage many more militants to look beyond easier, more accessible targets in the Middle East, Europe, and South-east Asia toward the "big score", a deadly attack on Mr Trump's America. Mr Trump's rhetoric will also make it easier for militant organisations to recruit and raise money. A more aggressive intervention in the Middle East's various conflicts would amplify that effect.
The greatest source of worry over a Trump presidency and foreign policy comes from the uncertainty they would create. There's a saying in Washington that "personnel is policy". In other words, to predict how a president might act, look not to what he says but to the people he appoints to key positions. Much of the US foreign policy establishment, including many in the Republican Party that Mr Trump will represent next month, have warned publicly against his candidacy. True to his temperament, Mr Trump has dismissed them as embittered losers. He promises to bring many new people into positions of power.
Combine Mr Trump's willingness to overturn assumptions about the use of American power with a relatively unknown cast of supporting characters and it's easy to see why much of the world will be holding its breath for the next five weeks.
- The writer is president of Eurasia Group and author of Superpower: Three Choices for America's Role in the World.
