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Why the stock market tumbled Wednesday, ushering in its worst start to a quarter in about 2 years


It has been an ugly stretch for U.S. stocks, which was capped by Wednesday’s more-than-830-point tumble for the Dow Jones Industrial Average. To recap: The Dow DJIA, -3.15% and the S&P 500 index SPX, -3.29% booked their worst one-day slumps since Feb. 8, while the Nasdaq Composite Index COMP, -4.08% put in its worst single-session skid since Brexit, when the U.K. voted to exit from the European Union, roiling global markets in 2016. Wednesday’s action wasn’t as severe as Brexit, but the downbeat action cast a pall over a rally that has mostly been driven by domestic economic strength and earnings that have been buoyed by corporate tax cuts. So, what’s next? And what has led to an apparent broad-based