President Donald Trump's attacks on the Federal Reserve spooked the stock market on Christmas Eve, and efforts by his Treasury secretary to calm investors' fears only seemed to make matters worse, contributing to another day of heavy losses on Wall Street.

The major stock indexes fell more than 2 percent Monday, nudging the market closer to its worst year since 2008. Stocks are also on track for their worst December since 1931, during the depths of the Great Depression.

The market has been roiled for most of the month over concerns about a slowing global economy, the escalating trade dispute with China and another interest rate increase by the Federal Reserve.

The past two trading days, however, have been dominated by something else: major losses following tweets from the president criticizing Fed Chairman Jerome Powell and the central bank.

Trump's Monday morning tweet heightened fears about the economy being destabilized by a president who wants control over the Fed.

"The only problem our economy has is the Fed," the president tweeted. "They don't have a feel for the Market, they don't understand necessary Trade Wars or Strong Dollars or even Democrat Shutdowns over Borders. The Fed is like a powerful golfer who can't score because he has no touch - he can't putt!"

Peter Conti-Brown, a financial historian at the Wharton School of the University of Pennsylvania, said: "We've never seen anything like this full-blown and full-frontal assault. This is a disaster for the Fed, a disaster for the president and a disaster for the economy."

On Sunday, Treasury Secretary Steven Mnuchin made a round of calls to the heads of the nation's six largest banks in an attempt to calm jitters, but the move only raised new concerns about the economy.

Most economists expect growth to slow in 2019, not slide into a full-blown recession. In fact, many economic barometers still look encouraging. Unemployment is at 3.7 percent, the lowest since 1969. Inflation is tame. Pay growth has picked up. Consumers boosted their spending this holiday season.

Fed board members are nominated by the president, but they've historically made decisions independent of the White House. Trump nominated Powell last year to become chairman.

But the president has voiced his anger over the Fed's decision to raise its key short-term rate four times in 2018. Those measures are intended to prevent the economy from overheating.

Trump's latest remarks only created more uncertainty for already unnerved investors who have seen all of this year's stock market gains evaporate.

"Now we're having a correction and we're down for the year, so the narrative people get drawn to is that perhaps his more unpredictable policies are bad for the market," said Craig Birk, chief investment officer at Personal Capital. "The separation between the president and the Fed, maybe just causes a little more concern than it would have a few months ago."

The S&P 500 index slid 65.52 points Monday, or 2.7 percent, to 2,351.10. The benchmark index is now down 19.8 percent from its peak on Sept. 20, close to the 20 percent drop that would officially mean the end of the longest bull market for stocks in modern history - a run of nearly 10 years.

The Dow Jones Industrial Average sank 653.17 points, or 2.9 percent, to 21,792.20. The Nasdaq skidded 140.08 points, or 2.2 percent, to 6,192.92. The Russell 2000 index of smaller-company stocks gave up 25.16 points, or 2 percent, 1,266.92.

Trading was choppy and volume was light Monday during a shortened trading session ahead of Christmas on Tuesday. U.S. markets will reopen on Wednesday.

Technology stocks, health care companies and banks took some of the heaviest losses in the sell-off.

Mnuchin said the heads of Bank of America, Citigroup, Goldman Sachs, JP Morgan Chase, Morgan Stanley and Wells Fargo all assured him they have ample money to finance their normal operations, even though there have been no serious liquidity concerns rattling the market.

Wells Fargo slid 3.4 percent, Microsoft 4.2 percent and Johnson & Johnson 4.1 percent.

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