A sense of déjà vu overwhelmed Wall Street this week, as Donald Trump’s election win gave the stock market a jolt similar to what happened after his victory eight years ago. Small caps soared, banks leaped and the S&P 500 Index had its best Election Day in history and strongest week in 12 months.

World shares are mostly lower after the Federal Reserve cut interest rates again to ease pressure on the U.S. economy.

All year, a slew of Wall Street pros have questioned the durability of an indiscriminate risk rally that has fattened stock prices by trillions of dollars, sent Bitcoin soaring, fueled a credit bonanza, and more. All year, besides a short-lived market ...