Wall Street billionaires are not used to being on the outside looking in. But that is where they find themselves after President Trump ignored their appeals to call off his tariff plans which they fear could endanger the economy.

With the backdrop of rapidly mounting stock market losses, corporate titans have worked every angle — phone calls, social media and even a typically staid shareholder letter — to try to change Mr. Trump’s mind.

The day after the president announced his most sweeping round of tariffs last week, chief executives from major banks, including Jamie Dimon of JPMorgan Chase, had a private meeting with Commerce Secretary Howard Lutnick organized by a lobbying group in Washington. But Mr. Lutnick was not persuaded to reverse course, three people briefed on the sit-down said.

Over the weekend, megadonors to Mr. Trump’s re-election effort tried a different tack, pleading their case in calls to Susie Wiles, the White House chief of staff, and Treasury Secretary Scott Bessent, people familiar with the calls said. Those efforts also came up empty.

By Monday, hedge fund billionaires — many of whom had been loud and proud boosters of Mr. Trump’s second term — were going public with their cries.

“The global economy is being taken down because of bad math,” the hedge fund manager William A. Ackman posted Monday morning on X. He added, “The President’s advisors need to acknowledge their error before April 9th and make a course correction before the President makes a big mistake.”