I would have thought it obvious: the US, since WWII, has, despite its flaws, represented to many the hope of democracy and a somewhat civilized, functional world order. There have always been autocrats in various nations that have been seen as threats to democracy and world order - but never before has there been an American president who has been widely seen as a threat to democracy and world order. Hence, the level of protest directed toward him - apart from his utter boorishness, which is a polite way of putting it.