The stock market Wednesday took its biggest dive since before President Donald Trump’s election, as investors began to grapple with the increasing possibility that Washington would be consumed with chaos and fail to enact policies to boost the economy.

The Dow Jones industrial average lost 372.82 points, or 1.8 percent, to 20,606.93, as a broad array of other indexes all lost ground.

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 Nasdaq composite index, coming off setting two consecutive highs, gave up 158.63 points, or 2.6 percent, to 6,011.24.

Meanwhile, a measure of volatility known as the VIX, which had been subdued in recent months, spiked by 21 percent, suggesting anxiety by investors about a sense of rising political risk in Washington.

The developments are an interruption to the slow-and-steady rise in market values since before Trump’s election. While the night of his surprise win in November created immediate uncertainty, with foreign markets selling off, they quickly regained their footing and resumed their yearslong climb. Investors cited new hopes that a Washington unified by GOP control would deliver an overhaul of the tax system and a large increase in spending on U.S. infrastructure — two of corporate America’s top policy goals.

The White House embraced the notion of a “Trump Rally.” But the disarray emanating from 1600 Pennsylvania Avenue now threatens to undermine those gains, as lawmakers, analysts and investors increasingly worry that it may impede the GOP agenda.

“Right now, we have a Congress that is likely to be consumed with other priorities,” said Brad McMillan, chief investment officer at Commonwealth Financial Network.

Stocks dropped and foreign currencies gained against the U.S. dollar Wednesday after reports that Trump reportedly asked then-FBI Director James Comey to drop his investigation into former national security adviser Michael Flynn’s relationship with Russia.

The market turbulence comes amid near-record highs following an eight-year bull run fueled by strong earnings. The stock market has been on a tear since the election.

“The latest controversy involving the Trump administration erodes confidence in his administration’s ability to enact tax reform,” said Michael Farr, who runs a Washington investment firm. “The prospect of significant tax reform has been buoying markets since President Trump was elected. We’ve had many controversies, but nothing has gotten the market’s attention. But once you start to go after tax reform, you are going to have the market’s full attention.”

Some have drawn comparisons between Trump’s troubles and those that brought down President Richard Nixon.

Investor unease over then-President Richard Nixon’s future as Watergate storm clouds gathered sent the stock market tumbling in January 1973. The S&P 500 didn’t fully recover for nearly eight years.