Billionaire investor Bill Ackman, who endorsed Trump’s 2024 presidential bid, warned yesterday that going ahead with the new tariffs was tantamount to launching an “economic nuclear war.”

Last Thursday, Trump said he would impose significantly higher “reciprocal” tariffs on dozens of countries that have the highest trade imbalances with the US.

Later in the day, billionaire Ken Fisher, the founder and executive chairman of Fisher Investments, said on X: “What Trump unveiled (last) Wednesday is stupid, wrong, arrogantly extreme, ignorant trade-wise and addressing a non-problem with misguided tools. Yet, as near as I can tell it will fade and fail and the fear is bigger than the problem, which from here is bullish.”

Fisher noted that he does not typically comment publicly on presidential actions, “but on tariffs Trump is beyond the pale by a long shot.”

Even Elon Musk – the world’s richest man and top Trump acolyte – said Sunday that he hoped for a “zero-tariff situation” between Europe and the US. In an interview with Italy’s Deputy Prime Minister Matteo Salvini via video link, Musk said he wanted to see an effective “free-trade zone” created between Europe and North America.

Echoing Ackman, Simon MacAdam, deputy chief global economist at consultancy Capital Economics, said businesses were likely to hold off making investments due, in large part, to the “sheer uncertainty” of Trump’s tariff policy.

“If you’re a mid-sized or even a large-cap company, you’re going to be very hesitant about what to do,” he told CNN.

“If those tariffs are going to be negotiated back down again in a few months’ time, then you’d be wasting your time investing potentially hundreds of millions of dollars in new plants… in the US.”

In his post, Ackman said the new tariffs were “massive” and “disproportionate,” saying: “This is not what we voted for.” He called for a 90-day “time out” in which Trump could negotiate with trading partners to “resolve unfair asymmetric tariffs deals.”

Trump has said his tariff agenda is designed to redress years of lopsided trade between America and its partners, caused, in his view, by other countries imposing steeper tariffs on US goods imported into their markets than the US does on theirs.

But investors are clearly not convinced by the wisdom of Trump’s plan. Stock markets in Asia and Europe plunged Monday and futures pointed to another bad day for US stocks, following Trump’s tariffs announcement last Wednesday.