Donald Trump says the problem in the United States is that "we don't win anymore." Trade is his favorite example, based on our longstanding trade deficit. But in one big area, America is a big global winner, year after year. That little-known fact exposes the basic, fatal error in Trump's lament. What he overlooks is that this country is one of the most inviting places for people abroad to invest their money. Since 2001, foreign direct investment in the United States has more than doubled. Last year, foreigners bought $11 trillion worth of stocks. They also wanted other assets --...