Stocks fell sharply as investors worried that the latest turmoil in Washington could hinder President Donald Trump's pro-business agenda.
The steep drop Wednesday was the market's worst since September and ended an unusually long period of calm.
Banks, which soared in the months since the election, slumped. Bank of America lost 5.9 percent.
Bonds, utilities and gold rose as traders shunned riskier assets. The dollar fell.
The Standard & Poor's 500 dropped 43 points, or 1.8 percent, to 2,357.
The Dow Jones industrial average lost 372 points, or 1.8 percent, to 20,606. The Nasdaq fell 158 points, or 2.6 percent, to 6,011, a day after its latest record high.
Small-company stocks, which would stand to benefit greatly from Trumps' proposed tax cuts, fell more than the rest of the market.