I got the election profoundly wrong, just like nearly everyone else. We can speculate about the Comey letter, about not enough Never Trumpers, not nearly enough Dem turnout in the key states, and on and on. Instead, I will focus on the ramifications for international relations.
When an earthquake hits, much of the damage occurs where there is liquefaction--where the earth underneath buildings and everything else becomes much more fluid. The US has long served, with some warts along the way, as the ground on which the international order rested: NATO, the World Bank, the International Monetary Fund, the various agreements and norms that facilitate trade, investment, peace and prosperity. Trump's election means that those institutions and practices no longer are on solid ground.
It does not mean that Trump will pull out of these institutions either immediately or ever. But it does meant that actors around the world can no longer be as certain about the international order--that the US would support the international order when it comes under stress. That an attack upon a NATO member might not lead to an American response. That a financial crisis might not lead to American efforts to shore up the countries or regions that are affected. And on and on. The big problem here is not the lack of response down the road--but the fear now that the US will not respond. Countries and other players will anticipate Trump's hedging/weakness, with some taking advantage (Putin) and others acting preemptively, perhaps causing significant crises (nuclear proliferation, perhaps).
People seemed to think the Obama administration did not lead enough, that it was a time of crisis and uncertainty. Well, just as one political scientist said that we would miss the Cold War, I am saying now that many will soon miss the Obama administration and even the Clinton-Obama-Bush era in US foreign policy. It was not perfect, but, as Dan Drezner entitled his book, The System Worked.