The S&P 500 ended March with its steepest monthly decline in more than two years, driven by uncertainty about the scope of President Donald Trump’s tariffs, which investors fear could accelerate inflation, slow consumer spending and stall the U.S. economy.

After a choppy session Monday in which the index ended higher for the day, the S&P 500 registered a 5.8% decline in March, its worst month since December 2022, when the Federal Reserve embarked upon a series of sharp interest rate increases as it sought to tame inflation. The decline in March caps off the S&P 500’s worst quarter at the start of a president’s term since President Barack Obama took over in 2009 during the financial crisis.

The benchmark is now down 8.7% from its mid-February peak, a downturn that is near a 10% “correction,” denting the values of portfolios and retirement funds across both Wall Street and Main Street. The technology-heavy Nasdaq Composite index, which has already slipped into a correction, ended the month down 8.2%.

Since taking office a little over two months ago, Trump has kept investors and companies guessing with a haphazard rollout of what he calls an “America first” trade policy. He has threatened, imposed and in some cases then paused the start of new tariffs on goods coming into the United States.

Whiplash over trade policy has fueled market volatility in the first few months of the year. Trump’s next round of tariffs, set to be unveiled Wednesday, could bring additional market swings in the coming days.

“That’s what the market is hoping for after April 2: Give us what you’re going to give us, tell us what’s going to happen, and we will then try to figure it out,” said Steve Sosnick, chief strategist at Interactive Brokers. “But until then, it’s very difficult to invest.”

Stocks had rallied in the wake of Trump’s election, buoyed by Wall Street’s hopes for deregulation and tax cuts. But the postelection rally lost steam as tariffs began to take center stage in Trump’s early economic policy priorities.

More recently, Trump has acknowledged but dismissed the potential financial hit to consumers and businesses from sweeping tariffs, eroding hopes that shaky markets would cause him to reconsider his actions.