What happens next? To judge by the comments of those gathered this week in Davos, Switzerland — where Prime Minister Mark Carney of Canada announced a “rupture” in the world order — nobody really knows. Europeans are surely scrabbling to make good on Mr. Trump’s climb-down. But after the shock of recent weeks, nobody should be in any doubt: NATO as we know it, the alliance that has been the bedrock of trans-Atlantic security for over 75 years, is coming to an end.