Why the world needs America as global policeman

The prospect of the return of Trump to the White House next year raises a huge question mark over the future of America's global leadership. In his first term, he flirted with pulling the US out of NATO. In a second term, he might actually go through with it. Indeed, if he pursued the most radical version of his "America First" ideology, a second Trump administration could see a complete break with the idea that it is in America's interests to underpin the security arrangements in three of the most strategic regions in the world — Europe, Northeast Asia and…