An upcoming U.S. Supreme Court ruling on the legality of the sweeping tariffs that President Donald Trump rolled out in April — briefly sending markets worldwide into a tailspin — could be the next test for stocks that have been flying high.

The S&P 500 Index has since rallied 39% from the lows hit that month. It closed at a record high Thursday, in part because tariffs have settled lower than Trump’s highest threats, while support has come from an artificial-intelligence investment boom and a U.S. economy that has kept expanding fast enough to throw off record corporate profits.

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