The Pershing Square hedge fund manager said the administration’s plans would result in an “economic nuclear war” and pleaded for a 90-day pause to allow space for negotiations with trading partners.

Amid economists pencilling in the growing risk of a global recession, even key allies such as Tesla CEO Elon Musk have pressed over the weekend for at least some level of détente. The far more punitive “reciprocal tariffs”—a misnomer, given that they are not based on tariffs set by the target countries—are set to take effect on Wednesday.

“By placing massive and disproportionate tariffs on our friends and our enemies alike and thereby launching a global economic war against the whole world at once, we are in the process of destroying confidence in our country as a trading partner, as a place to do business and as a market to invest capital,” Ackman wrote on social media on Sunday. 

The billionaire, who used Musk’s X (where he has 1.7 million followers) to endorse Trump, was so frustrated at the administration’s policies that he accused commerce secretary Howard Lutnick of personally loading up on bonds to benefit from the stock market sell-off. (He later apologized to Lutnick, the former CEO of investment bank Cantor Fitzgerald).

Ackman’s emotive appeal briefly to prevent “a self-induced, economic nuclear winter” seemed to work when Trump economic advisor Kevin Hassett appeared to say on Fox News that Trump was open to the idea of postponing the plan by three months, with the exception of China. That immediately lifted sentiment on Wall Street—until the White House then denied the rumor.

Trump followed that up with a post on Truth Social that he would impose an additional tariff of 50% on China from Wednesday, on top of last week’s 34% hike, if Beijing did not drop its reciprocal 34% tariff by Tuesday, April 8.

‘We will severely damage our reputation with the rest of the world’

Permanent tariffs are widely acknowledged to have a place in global trade if they are intended to protect a handful of individual countries’ key strategic industries. But Trump has remained vague about his actual intentions behind the across-the-board hike.

Some in his administration claim they are permanent, while others including have suggested they are means of pressuring countries into negotiating a deal. Some argue they are designed to re-shore manufacturing plants, while others claim they are a tool to raise revenue.

The confusion over the ultimate goal was exacerbated by a decision to base retaliatory tariffs on trade deficits rather than establishing reciprocity on tariffs. Even more inexplicably, the White House then issued a denial, claiming that was not the case, while then providing a mathematical equation that proved just that.

“The formula used by the administration to calculate tariffs made other nations’ tariffs appear four times larger than they actually are,” Ackman continued. 

Keeping markets guessing may be a tactic that results in a better overall outcome ultimately. The European Union has already offered to drop tariffs on industrial goods to zero should the U.S. follow suit, while Taiwan said it has no plans to adopt retaliatory tariffs.

In the short term, businesses are expected to freeze investments and hiring until the clouds clear, risking a globe-spanning recession. 

“If on the other hand, on April 9th we launch economic nuclear war on every country in the world, business investment will grind to a halt, consumers will close their wallets and pocket books, and we will severely damage our reputation with the rest of the world that will take years and potentially decades to rehabilitate,” Ackman said.