The growing political drama in Washington rattled Wall Street Wednesday, knocking the Dow Jones industrial average down more than 370 points and giving the stock market its biggest single-day slump in eight months.

Investors worried that the headline-fueled political turmoil that has enveloped the White House may hinder President Donald Trump’s plans to cut taxes, roll back government regulations and other aspects of his pro-business agenda.

“When you are at these valuations, the market has to reassess whether or not the agenda is actually going to be implemented,” said Quincy Krosby, market strategist at Prudential Financial. “What you’re seeing is a classic run toward safety.”

The steep drop ended an unusually long period of calm for the markets, which had been hovering near all-time highs.

Financial stocks, which had soared in the months since the election, declined the most as bond yields fell sharply.

Bonds, utilities and gold rose as traders shunned riskier assets. The dollar fell.

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The Standard & Poor’s 500 index had its biggest drop since September, sliding 43.64 points, or 1.8 percent, to 2,357.03.

The Dow lost 372.82 points, or 1.8 percent, to 20,606.93. The Nasdaq composite index, coming off setting two consecutive record highs, gave up 158.63 points, or 2.6 percent, to 6,011.24.

Small-company stocks fell more than the rest of the market. The Russell 2000 index sank 38.79 points, or 2.8 percent, to 1,355.89. Those companies would stand to benefit even more than large ones from corporate tax cuts Trump is proposing. They also had risen sharply in the months following the election.

The seeds of Wednesday’s steep market sell-off were present late Tuesday, when a published report revealed that Trump allegedly made a personal appeal to now-fired FBI Director James Comey to drop the bureau’s investigation into former National Security Adviser Michael Flynn. The White House denied the report.

“The controversy is not new, but this one really seems to be sticking,” said Erik Davidson, chief investment officer for Wells Fargo Private Bank. “The Trump economic program is either going to be delayed by this turn of events or possibly be derailed, that’s why investors are acting the way they are.”