Trump tried and failed to build a wall in Ireland. That could mean big trouble for Europe.

Before Donald Trump proposed a 1,000-mile wall on the U.S.-Mexico border to stop migrants, he tried to build a two-mile barrier on a pristine stretch of Irish coast to rein in an ocean.

He didn’t succeed. 

Irish surfers, weekend beachcombers, environmental scientists, local planners and even a microscopic snail got in his way. In December, Trump International Golf Links backed down from plans it had said were essential to protect the company’s lone Irish course — picturesquely nestled in dunes overlooking the Atlantic — from being swallowed by rising seas. 

For a man who loves to win, the defeat — just a month after his election as president — has left a bitter taste. And despite the motley nature of the resistance, Trump seems to have singled out a lone culprit: the European Union, whose rules and regulations underpinned many of the objections.

In interviews and public statements, Trump has cited his tangle over the golf-course wall as Exhibit A in justifying a jaundiced view of the E.U. that puts him at odds with decades of bipartisan U.S. foreign policy. 

Previous presidents — Democrats and Republicans alike — have seen the E.U. as an essential partner in global stability and a bulwark against the self-interested nationalism that spawned two world wars. To Trump, the bloc’s environmental protection regulations were a threat to his exquisitely manicured fairways and putting greens. 

“I found it to be a very unpleasant experience,” he told British and German interviewers last month after bringing up the wall dispute, unbidden, when asked his opinion of the E.U.

“A very bad experience,” he emphasized weeks later as he raised the issue at his first White House news conference.

The bureaucratic battle over a golf-course sea wall makes for an unlikely inflection point in geopolitical history. And yet in Europe, Trump’s hostility toward the union that backers credit with keeping decades of continental peace is seen as a potentially fatal blow. 

European Council President Donald Tusk recently took the extraordinary step of including Trump on a list of threats to the already teetering E.U., right alongside China, Russia and radical Islam.