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President Donald Trump on Wednesday said the stock market's worst month since 1931 was due to a "glitch."

Trump told reporters on the first trading day of 2019 that after December's near-historic sell-off, stocks would rise once his trade deals have been resolved.

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Following a turbulent month that capped a roller-coaster year on the stock market, the Dow Jones Industrial Average opened down 350 points on Wednesday, before leveling out by mid-afternoon.

“Everybody is terrified that this is a sign of a global slowdown,” Art Cashin, director of floor operations at UBS, told CNBC, responding to economic data that indicated China's manufacturing activity is showing signs of decline. “It was only eight months ago we were talking about synchronized growth and all of that is falling apart.”

Trump has expressed repeated ire over the stock market swings, laying the blame for a down market with Federal Reserve Chairman Jerome Powell. Trump said last month the Fed head needed to "feel the market" instead of raising the central bank's benchmark borrowing rate four times last year.

Although December is usually a quiet month for markets, 2018 marked the worst December for stocks since 1931, and all major indexes saw their worst yearly performances since the financial crisis. The S&P 500 was down 6.2 percent for 2018, the Dow declined by 5.6 percent, and the Nasdaq fell by 3.9 percent, its worst annual performance since 2008.

Market volatility was fueled last year by months of tit-for-tat billion-dollar trade skirmishes between the U.S. and its major trading partners, with China finally agreeing to a 90-day cease-fire while negotiations continue.

“Unless you expect a recession [or] total financial crisis, the level of volatility will probably drop down in the next few months,” Ian Harnett, chief investment strategist at Absolute Strategy in London, told NBC News, although he added the caveat that volatility in 2019 will likely be greater than it was in 2018.