President Donald Trump's tariff battle suffered a major defeat Friday when a federal appeals court ruled that his most extensive tariffs were illegal, saying he overstepped his authority. And Nobel Prize-winning economist Paul Krugman expressed "shock."

The court found that the law Trump used to hand down steep tariffs did not grant him the power to enforce them. The ruling's implementation was suspended until Oct. 14, however, to allow the administration to appeal to the Supreme Court.

The ruling challenged Trump's use of emergency powers for trade deficit and other economic concerns.

Writing on his blog, Krugman reacted to the ruling writing, "Holy tariff mess, Batman."

"Wow. An appeals court, backing up the Court of International Trade, has just ruled the majority of Trump’s tariffs illegal. We kind of knew this was coming, but the reality still comes as a shock," he said.

Krugman emphasized that the court didn't find the tariffs were unlawful; rather, the way Trump went about implementing them was, specifically, by claiming an economic emergency.

"But just saying 'I am the Tariff Man, and here are my tariffs' isn’t OK," remarked Krugman.

The former New York Times columnist pointed out that the president is declaring an economic emergency while simultaneously proclaiming the economy has never been stronger.

"So how can things both be terrific and an emergency calling for drastic action?" he asked.

Krugman then mocked the president over his furious reaction on Truth Social, in which he declared the ruling, if upheld, would "literally destroy" America.

"Take away these tariffs, and the county will revert to the blasted wasteland it was on … April 1, just before Trump made his big tariff announcement," he wrote.

Krugman conceded that an "utterly craven" Supreme Court could hand Trump an eventual win — or they could "balk." Either way, Krugman called it a "self-inflicted disaster," since Trump could have just had Republican lawmakers vote on the tariffs.

He concluded that if the tariffs are ultimately declared illegal, it won't embarrass America, as Treasury Secretary Scott Bessent has claimed.

"It will embarrass Trump and Bessent. If anything, it might reassure the rest of the world that some vestige of rule of law yet remains in this nation," he said.