Twenty-nine years separate these two statements by two U.S. presidents:

“Mister Gorbachev: Tear down this wall,” then-Republican President Ronald Reagan called out on June 12, 1987 in front of the Brandenburg Gate in Berlin to Soviet Chairman Mikhail Gorbachev.

May 25, 2016: “Build that wall! Build that wall!” Donald Trump, then a Republican candidate for U.S. president, chanted this slogan at an election rally in Anaheim, California. The wall is Trump’s most important campaign promise, but at present, there exist only about 350 miles of noncontiguous fence along the U.S.-Mexico border of approximately 2,000 miles. To avoid jeopardizing his chances for re-election in 2020, Trump is now taking his chances with a partial government shutdown that began on Dec. 22.

For Trump, the wall is the perfect solution to dealing with the anxiety of his base: for these voters, the “outside” threatens the supposedly sacred world inside. The more uncertain and confusing the times become and the blurrier the picture of reality gets, the greater their need for custody, clarity and a clear-cut definition of both sides. The wall is the solution for Trump fans: these people want “it” -- that ambiguous threat from outside -- to stop, to be kept out. The thickest and tallest possible divider, ideally made from reinforced concrete, has to come between them and a world that they more and more frequently associate with chaos. Trump’s promise is that we will finally have peace when this wall stretches from San Diego to the mouth of the Rio Grande into the Gulf of Mexico.

It’s nonsense, but Trump doesn’t care. He doesn't deal in fact-based solutions to political challenges, but in the politics of emotions.

And Trump is a trend surfer on the issue of wall-building. The European Union has also constructed some 620 miles of new border fences and walls since the fall of the Berlin Wall. In 1990, there were two fortified borders in the EU; in 2017, there were 15. Ten of the EU’s 28 current member states from Spain to Latvia have built more fences and walls since then.

The world finds itself in a dramatic phase of deglobalization and fragmentation, and walls are one symptom of this era.

Journalist Tim Marshall wrote in the conclusion of his recently published book, “The Age of Walls,” about his hope that the era of wall construction will be followed by an age of bridge-building.