President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE claimed early Thursday morning that stock markets would crash if he were impeached.

"If they actually did this the markets would crash," the president tweeted, just hours before the acting director of national intelligence's public testimony before Congress.

"Do you think it was luck that got us to the best Stock Market and Economy in our history," he added. "It wasn’t!"

If they actually did this the markets would crash. Do you think it was luck that got us to the best Stock Market and Economy in our history. It wasn’t! https://t.co/V0WGVWEWTN — Donald J. Trump (@realDonaldTrump) September 26, 2019

House Democrats formally launched an impeachment inquiry Tuesday evening following reports that Trump asked Ukraine's president to investigate former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE and his son Hunter Biden.

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The White House released a partial transcript of the call on Wednesday, confirming the request from Trump and revealing that Trump encouraged Ukrainian President Volodymyr Zelensky to work with his personal attorney and the attorney general to investigate the unsubstantiated allegations.

Amid reports that impeachment was on the horizon, the Dow Jones dropped 0.5 percent, the S&P 500 slipped 0.8 percent and the Nasdaq composite dropped 1.46 percent on Tuesday.

While Tuesday marked the worst day for the S&P 500 and Nasdaq in a month, markets rebounded Wednesday and almost reached Monday's levels.

During the last two impeachment inquiries, for former Presidents Bill Clinton William (Bill) Jefferson ClintonHarris: Ginsburg 'absolutely' cleared the path for me Anxious Democrats amp up pressure for vote on COVID-19 aid Barr's Russia investigator has put some focus on Clinton Foundation: report MORE and Richard Nixon, stocks fell. But economists have argued the dips were largely driven by outside factors including runaway inflation and the Asian currency crisis.

The U.S. economy has recently been affected significantly by the trade conflict between the U.S. and China.