"In abandoning Europe we would be abandoning not only the fountainheads of most of our own culture and traditions; we would also be abandoning almost all the other areas in the world where progressive, representative government is a working proposition. We would be placing ourselves in culturally and politically. To traditions and institutions, we loudly in the dark. I am not sure the position of a lonely country, maintain confidence in our own would henceforth have to whistle that whistling could be loud enough to do the trick.
I know that there are many people--and probably some among you--who will reply indignantly that I am selling short the strength and soundness of our institutions, and who will maintain that American democracy has nothing to fear from Europe's diseases and nothing to learn from Europe's experiences.
I wish I could believe that were true. I wish I could believe that the human impulses which give rise to the nightmares of totalitarianism were ones which Providence had allocated only to other peoples and to which the American people had been graciously left immune. Unfortunately, I know this is not true. After all, most of us are Europeans once or twice removed; and some of us are less removed than that. There are openly totalitarian forces already working in our society...And it is not even with these small existing groups of extremists that the real danger lies. The fact of the matter is that there is a little bit of totalitarian buried somewhere, way down deep, in each and every one of us. It is only the cheerful light of confidence and security which keeps this evil genius down at the usual helpless and invisible depth. If confidence and security were to disappear, don't think that he would not be waiting to take their place. Others may lull themselves to sleep with the pleasing assumption that the work of building freedom in this country was accomplished once and for all by our forefathers. I prefer to accept the word of a great European, the German poet Goethe, that freedom is something that has to be reconquered every day. In that never-ending process of re-conquest, I would hate to see this country lose all its allies.
--- Measures short of war / George Kennan (1947)
totalitarianism today notes that Kennan "worried that the rise or expansion of communism into Western Europe would give American extremists cause to enact illiberal legislation"
They continue:
"Kennan made these remarks at a time when popular fear of communism was threatening to overwhelm sound policy deliberation. In a sense, such a threat challenges democracies following periods of crisis-- the fear trumps the reasoning, the emotions overwhelm the mind"
In light of this, Trump Derangement Syndrome and the Nazi Moral Panic's parallels with McCarthyism (which started just a few years after Kennan's speech) are even more evident.
Ironically, Popper would not have tolerated all those people who keep ranting about punching "Nazis" and boasting that they won't talk to them - all the while invoking the paradox of tolerance.