Previous American presidents supported despots for reasons of cold-war realpolitik. ( “He's a bastard, but he's our bastard,” as Harry Truman is reputed to have said of an anti-communist tyrant in Nicaragua. )
Mr Trump's attitude seems more like: “He's a bastard. Great!”
This repels America's liberal allies, in Europe, East Asia and beyond.
It emboldens autocrats to behave worse, as in Saudi Arabia this week, where the crown prince's dramatic political purges met with Mr Trump's blessing.
It makes it easier for China to declare American-style democracy passe, and more tempting for other countries to copy China's autocratic model.
The idea that things will return to normal after a single Trump term is too sanguine.
The world is moving on.
Asians are building new trade ties, often centred on China.
Europeans are working out how to defend themselves if they cannot rely on Uncle Sam.
And American politics are turning inward: both Republicans and Democrats are more protectionist now than they were before Mr Trump's electoral triumph.
For all its flaws, America has long been the greatest force for good in the world, upholding the liberal order and offering an example of how democracy works.
All that is imperilled by a president who believes that strong nations look out only for themselves.
By putting “America First”, he makes it weaker, and the world worse off.