Financial markets were hit by another wave of selling on Sunday evening, with investors and economists grappling with rising odds of a severe economic downturn caused by President Trump’s significant new tariffs on imports.

Futures on the S&P 500, which allow investors to bet on the index before the official start of trading on Monday, dropped roughly 4 percent on Sunday evening. In oil markets, which also open for trading on Sunday evening, prices fell more than 3 percent — adding to steep losses last week. And the price of copper, considered a broad economic indicator, slid more than 5 percent.

The 10.5 percent drop in the S&P 500 on Thursday and Friday was the worst two-day decline for the index since the onset of the coronavirus pandemic in 2020.

The only other instances of a worse two-day drop came during the 2008 financial crisis and the 1987 stock market crash, according Howard Silverblatt, senior index analyst at S&P Dow Jones Indices. In dollar terms, the more than $5 trillion that was wiped out in the S&P’s value in the two days last week stands unmatched.

Even more unusual is that last week’s sell-off stemmed directly from presidential policy. Mr. Trump has so far brushed off concerns about the market reaction and potential economic consequences, showing little intention of backing down.

“If they’re maintained, the tariff hikes announced April 2 represent a self-inflicted economic catastrophe for the United States,” Preston Caldwell, senior US economist for Morningstar Research Services, said in a blog post on Friday.

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