U.S. stocks plummeted following an ABC report that former national security adviser Michael Flynn will testify against President Trump in the Russia investigation.

For the day, the S&P 500 Index is down more than 1 percent, the most in three weeks, though it rebounded a bit shortly before noon.

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The Dow Jones index suffered a similar fall; it was down more than half a percent at midday.

Stocks really fell after 11 a.m., shortly after ABC reported that Flynn would testify against Trump.

MORE: Michael Flynn "is prepared to testify...against Pres. Trump, against members of the Trump family, and others in the White House," @BrianRoss reports. https://t.co/aiagnvIJDs https://t.co/yuVw9iDrKp — ABC News (@ABC) December 1, 2017

Stocks have been rising as part of a long bull market and topped 24,000 for the first time on Thursday.

The market has grown since Trump took office, rising above 20,000 for the first time earlier this year as traders made bets on corporate growth from tax cuts and deregulation from Trump.

Trump has repeatedly praised the booming stock market and taken credit for its success, telling reporters last month that, “the reason our stock market is so successful is because of me."

The Senate is expected to pass its tax-cut package on Friday, which would reduce the corporate tax rate from 35 percent to 20 percent.

The bill will then need to be reconciled with a different House measure before legislation can be sent to the White House.

Flynn was charged Friday with making false statements to the FBI.