If you think history repeats itself, consider this: For the last 73 years, the Western alliance has been led by the nations that defeated Nazi Germany, foremost among them, the United States. For the last year or so, it has been led by the former Nazi Germany, reformed and reconstituted as a liberal democracy. The U.S., it is fair to say, has been going the other way.

Now both are converging. German chancellor Angela Merkel has reluctantly come to grips with the political cost of her admirable migrant policy, promising a sterner application of the laws and closing the door a bit to what had been the flood of Middle Eastern political refugees. She acted after politicians to her right threatened to pull out of the government. They want to make Germany great again.

Off to the side, tweeting in a juvenile fashion, is Donald Trump. Instead of giving Merkel support, even some sympathy, Trump has been belittling her. In characteristic fashion, he's got almost everything wrong, including alleging an upsurge in crime in Germany committed by Middle Eastern immigrants. Actually, crime is down, but the facts never mattered to Trump. His crime wave is like his inaugural crowd and his own greatness -- real only to him.

Merkel is an entirely commendable political leader. When she called on her fellow Germans to welcome nearly 1 million migrants and refugees in 2015, she had the best of intentions. But being a good person is not the same as being a wise leader. It's now clear that Merkel sorely tested Germany's tolerance and hospitality. There's been a backlash. Bavaria, in particular, has had it up to here with migrants. So, too, have nearby countries. The principle of a borderless Europe is gasping for air. Barriers are going up.

Any other American president would have lamented the possible end of a borderless Europe. Any other American president would have recognized that Merkel was doing the humane thing in admitting so many migrants and would have offered moral support. Any other American president would recognize that once history starts marching backward, there's no telling where it will stop. A borderless Europe, after all, was intended to deal with the disease of virulent nationalism. Twice in the last century, Europe took the world to war. This is a continent that knows how to fall off the wagon.

At the heart of Europe is Germany. It is the continent's most important country, its largest economy, its most populous country. Its eastern neighbors -- Austria, Poland and Hungary -- have moved to the right. In Poland and Hungary's case, they're creeping up on authoritarianism. This is nothing new for these countries. They both had illiberal regimes before World War II. They seem to be heading that way again. Germany, too, has a past. Germany, in fact, has the past. It has faced it commendably. It cannot, though, eradicate it. Germany bears watching.

The U.S., too, is undergoing an ugly fit of nostalgia. Trump's anti-migrant demagoguery -- a nonexistent crime wave, for instance -- is reminiscent of the period from 1917 to 1921 when America entered World War I and communists took over Russia. Combined, these events caused Congress to lose its head and mop the floor with the Constitution. Speakers, writers, union leaders and others were arrested, jailed and in some cases deported to the emerging Soviet Union. An imminent threat was seen from Moscow, only 4,857 miles away. The Reds were coming. Now it's migrants -- a threat so dire that children had to be taken from their parents.

The worldwide resurgence of cruel folly is being cheered by the American president. He knows nothing of history. He does not know the reason Europeans with a memory cherish open borders. He does not know why they fear the right. He does not know why, to them, the vilification of the other, the outsider, is not something new, but an echo. The original sound never fully faded. Now the volume is being raised.

The migration phenomenon is bigger than any single world leader -- and that has to include any American president. But this president has only made things worse, cheering the haters and tossing spit balls at those, like Merkel, whose fault was an excess of what she called "Europe's basic principle: humanity." Trump kicked her while she was down, bringing to mind what Franklin D. Roosevelt said when Fascist Italy declared war on a France already attacked by Germany: "The hand that held the dagger has struck it into the back of its neighbor."

(c) 2018, Washington Post Writers Group