It is an axiom often heard in business school lecture halls and on corporate earnings calls: Uncertainty is bad for business.

The U.S. economy is about to test that proposition like never before.

The first weeks of the second Trump administration have been a whirlwind of economic policy moves: A spending freeze was declared, then rescinded. Federal programs, and even entire agencies, have been suspended or shut down. Tariffs have been threatened, announced, canceled, delayed or enacted — sometimes in a matter of days or even hours. Measures of economic policy uncertainty have soared to levels seen in recessions and global crises.

Business leaders — some who cheered President Donald Trump’s reelection, expecting lower taxes and reduced regulation — have been left shaking their heads.

“Your guess is as good as mine what’s happening in Washington,” said Nicholas Pinchuk, CEO of the toolmaker Snap-on.

“So far, what we’re seeing is a lot of costs and a lot of chaos,” Jim Farley, the CEO of Ford Motor, told investors this week.

“It’s like your head is spinning with what’s coming down; you just never know,” said Chad Coulter, founder and CEO of Biscuit Belly, a chain of breakfast restaurants based in Louisville, Kentucky.

Yet for all their concerns, the three CEOs say they are pushing ahead with planned investments and that they feel good about their prospects. So do many of their peers: Measures of business confidence soared after the election, and while there are hints that gleam has dulled to some degree, business leaders, as a group, remain upbeat.

A gauge of small-business sentiment from the National Federation of Independent Business ticked down in January but remained higher than in any month in the Biden administration.

“You’ve really got a battle between greater business optimism and greater business uncertainty, and they’re kind of opposing forces,” said Nicholas Bloom, a Stanford University professor who has studied how uncertainty affects the economy.

But even business leaders generally sympathetic to the new administration warn that confidence could fade if the turmoil in Washington doesn’t calm down relatively quickly — especially if Republicans seem to be struggling to reach deals on their legislative priorities.

Economists in recent years have tried to study the effect of uncertainty with academic rigor, developing measures to assess the phenomenon over time and across countries. Their research has found that uncertainty makes businesses more reluctant to hire and invest, and leads to lower sales, beyond the policies’ impact.

“Uncertainty itself is harmful to business activity,” said Steven Davis, a Stanford economist. When rules change, even in harmful ways, businesses can typically adapt, he said. But when rules aren’t clear, businesses can find themselves in limbo.