As America's friends and allies look on in astonishment at the all-but-certain prospect of a contest between Hillary Clinton and Donald Trump in November's U.S. presidential election, they need to do more than just wring their hands. They must hope for the best but prepare for the worst.
The crucial point about the 2016 election is not just that a reality-TV star and property magnate who has never held elected office has emerged as the presumptive Republican candidate. It is the enormous difference that a victory by Trump would make for the rest of the world compared with a victory by Clinton.
In every U.S. presidential election in modern times, America's friends and allies have had their private preferences. But never before have the Democratic and Republican candidates been as different as chalk and cheese. There was no unbridgeable gulf between Reagan and Carter, or Clinton and Bush, or Bush and Gore, or Obama and McCain. There is between Trump and Clinton.