WASHINGTON — President Donald Trump responded swiftly to a major Supreme Court setback, promising a backup plan to salvage his tariff regime. The high court struck down the duties Friday, declaring them invalid under the International Emergency Economic Powers Act, or IEEPA, which Trump had invoked to impose them.

Trump made the comments during a White House appearance minutes after the 5-4 decision landed. “We’re not done yet,” he told reporters. “We have a strong backup plan in place. My team is already looking at other legal paths to keep these tariffs where they protect American workers.”

The ruling centered on tariffs Trump announced in early 2025 targeting imports from China, Mexico and the European Union. Critics, including affected industries and trading partners, challenged the moves in federal court last year. Lower courts upheld some injunctions, sending the case to the Supreme Court on an expedited basis.

Chief Justice John Roberts wrote the majority opinion. He argued that IEEPA grants the president authority over economic emergencies abroad but does not extend to broad trade restrictions without congressional approval. “The statute’s text and history limit its scope,” Roberts wrote. “These tariffs exceed that authority.”

Dissenting justices, led by Clarence Thomas, called the decision a dangerous overreach. Thomas wrote that IEEPA gives the executive flexibility to counter foreign threats, including unfair trade practices. The tariffs, he noted, aimed to address national security risks from supply chain dependencies.

White House officials confirmed the backup strategy would rely on lesser-known statutes, such as Section 232 of the Trade Expansion Act of 1962. That provision allows tariffs for national security reasons. “We’ll pivot quickly,” Press Secretary Karine Jean-Pierre said. “The president remains committed to fair trade.”

Markets reacted sharply. The Dow Jones Industrial Average climbed 1.2% in afternoon trading, while the yuan strengthened against the dollar. U.S. manufacturers praised the ruling. The American Apparel & Footwear Association called it “a victory for consumers tired of higher prices.”

Trump’s tariff push began in his second term, escalating a trade war started during his first presidency. He imposed duties on $500 billion in goods, citing economic threats from abroad. The Supreme Court case, Trump v. U.S. Chamber of Commerce, drew briefs from 28 states and dozens of business groups.

Legal experts expect further litigation. Harvard Law professor Laurence Tribe predicted administration lawyers would file emergency motions by Monday. “They’ll test every angle,” Tribe said in an interview. Congressional Democrats, meanwhile, urged Trump to drop the fight. House Speaker Nancy Pelosi said the ruling exposes the limits of executive power.

The decision marks the court’s second major rebuff to Trump’s trade agenda this year. In March, justices limited his use of emergency funds for border wall construction. Trump dismissed that loss as minor. Sources close to the president say he views tariffs as central to his economic legacy.

Trading partners watched closely. A Chinese Commerce Ministry spokesman welcomed the ruling but warned of retaliation if duties return under new pretexts. EU Trade Commissioner Valdis Dombrovskis called for talks to avoid escalation.

As Trump plots his next move, aides emphasized speed. “We move fast,” one official said. “Backup plans are ready.” The president ended his remarks with a jab at the court. “Some justices forgot who’s fighting for America.”