America’s top court dealt a traumatic blow to Donald Trump’s second term in office on Friday, striking at the heart of his economic plans by ruling most of his tariffs illegal as the president lashed out at “disloyal” justices beholden to “foreign interests”.

The 6-3 Supreme Court opinion authored by Chief Justice John Roberts was damning for Trump, halting his flagship trade policy and setting new constraints on his use of executive power, which he has sought to expand since returning to the White House last year.

The president berated the justices as “disloyal to our constitution”, vowed to continue his trade wars, and announced another 10 per cent global tariff to come into force next week, threatening more turmoil and uncertainty.

But those levies are time-limited and his administration now faces the possibility of being compelled to repay billions of dollars raised by his invalidated tariff regime.

The ruling, ahead of next week’s State of the Union address, comes on the heels of disappointing GDP data and consistently poor approval ratings for the president that have raised alarm bells among Republicans about their prospects in the November midterm elections.

It also marked the latest sign of expanding resistance to Trump and his plans both domestically and internationally, from fellow western leaders balking at his threats against Greenland, to members of Congress forcing the release of documents related to late child sex offender Jeffrey Epstein, to Federal Reserve chair Jay Powell fighting a criminal probe against him as an attack on the central bank’s independence.

The ruling was especially potent given the Supreme Court’s conservative majority, which has given Trump broad latitude to act with fewer restraints in other areas, including his immunity from prosecution and his immigration crackdown.

But on trade policy, the court drew a clear red line in the opposite direction, saying that the president’s use of emergency tariffs, which he deployed extensively to reshape America’s relationship with the global economy and wield diplomatic leverage over countries, had violated the US constitution.

“It’s a huge blow to the centrality of how he thinks about his power . . . to try to bully other countries into making deals with him,” said Sarah Binder, a professor of political science at George Washington University. “The Supreme Court in one fell swoop said ‘not so quick, not so easy’.”

Although oral arguments in the case late last year had suggested that the court was leaning against Trump’s tariffs, his reaction was vitriolic.

The justices were “fools and lapdogs” as well as “unpatriotic and disloyal”, Trump said at a hastily arranged press conference at the White House. The president alleged that they were “swayed by foreign interests” and said other countries were “dancing in the streets”.

“I’m ashamed of certain members of the court, absolutely ashamed for not having the courage to do what’s right for our country,” he said.

The clear limits imposed on Trump’s power will bruise his ego, just as he seeks to put his personal stamp on Washington. He has added his name to the Kennedy Center and demolished part of the White House to build a new ballroom. On Thursday, the Department of Justice unfurled a large banner of the president’s face on its headquarters.

It also marks a humbling moment for Trump as he weighs a war on Iran — weeks after launching a special operations raid on Venezuela and seizing control of the country’s oil — defying the constitutional authority of Congress to approve the use of force against US enemies.

Julian Zelizer, a professor of political history at Princeton University, said the tariff ruling was “the biggest decision thus far, rebuking his expansive vision of presidential power”.

Zelizer added: “Does this mean that the imperial presidency has been restrained? No. Other Supreme Court decisions have empowered him and he will now try to find new paths to achieve the same goals. But this comes at a moment when there is significant pushback against his administration in many levels of government.”

The Supreme Court’s opinion leaves Trump scrambling to implement a backup plan to use other legislation to preserve some tariffs. The 10 per cent tariff he announced on Friday is based on section 122 of a 1974 law that allows the president to set import restrictions for up to 150 days.

He also vowed to launch new trade investigations that could lead to further tariffs later, and defiantly said that these could be even more severe than the regime struck down as illegal by the court.

Already, US businesses are gearing up to demand refunds from the Trump administration — payments that could deepen the US’s fiscal problems.

According to the Budget Lab at Yale, tariff revenue based on emergency powers was $142bn in 2025 — about 80 per cent of its estimate for all new tariff revenue raised last year.

Trump waived away the imminent threat of repayments. “They take months and months to write an opinion and they don’t even discuss that point,” he told reporters. “We’ll end up being in court for the next five years.”

The president’s political career has been shaped by his unapologetic embrace of tariffs, defying mainstream Republican orthodoxy in a bid to protect American workers left behind by globalisation.

He used established US trade laws to launch battles against China and others in his first term, but in his second term the president has taken his protectionist agenda to a new level, including using emergency powers to impose the taxes.

“It’s our declaration of economic independence,” Trump exclaimed on his so-called liberation day last April, as he set high tariffs that rattled global markets.

Within a few weeks, Trump paused many levies in the face of the market turmoil, and then watered them down with trade agreements and exemptions.

On Friday, he was confronted with the sobering legal defeat.

“The president took a serious risk in using [emergency powers] as the legal basis for many of his tariff threats and hikes, and this gamble did not pay off,” said Wendy Cutler, a former US trade official and senior vice-president at the Asia Society Policy Institute.

Even some Republicans appeared relieved that the justices had set boundaries on the president.

“The founders’ system of checks and balances remains strong, nearly 250 years later,” said John Curtis, the Republican senator from Utah.