Not content with rewriting the rules of international trade, U.S. President Donald Trump has sought to upend a vital cornerstone of the U.S. financial architecture: the independence of the Central Bank. Mr. Trump has deemed the chair of the Federal Reserve, Jerome Powell, a “loser” for refusing to lower interest rates. Though he has walked back his threat of firing Mr. Powell, the U.S. President’s interference has deepened uncertainty in global financial markets.