In a major rebuke of President Donald Trump's signature economic policy, the U.S. Supreme Court has struck down the vast majority of his sweeping tariff regime. In a 6-3 ruling, the nation's highest court decisively ruled that the president exceeded his legal authority in unilaterally imposing tariffs on imports from nearly every country under the guise of national security.

A Stinging Defeat for Trump

What this really means is a huge setback for Trump's broader economic agenda. The President has repeatedly used tariffs as a cudgel, aggressively taxing imports in an effort to boost American manufacturing and reduce trade deficits. But the Supreme Court has now made it clear that the law he invoked - the International Emergency Economic Powers Act (IEEPA) - does not grant him the power to impose such far-reaching tariffs.

As Reuters reports, the 6-3 ruling authored by conservative Chief Justice John Roberts declared that the IEEPA statute "does not embrace the power to impose tariffs." The decision upholds a lower court's finding that Trump acted unlawfully in using the IEEPA, which was intended for use in true national emergencies, as the basis for his sweeping tariff regime.

Uncertainty Ahead for Trade Agreements

The bigger picture here is that this ruling could generate significant uncertainty around various trade deals the U.S. has struck in recent years. As SCOTUSblog notes, Justice Brett Kavanaugh warned in his dissent that the decision "could generate uncertainty regarding various trade agreements" worth trillions of dollars.

And while the court did not weigh in on the issue of refunds for importers who paid the illegal tariffs, estimates suggest the government may be on the hook for over $200 billion in such payments.

So in the end, this ruling represents a major blow to Trump's broader economic vision - one that has relied heavily on the aggressive use of tariffs to reshape global trade. The President was quick to lash out at the court, but his options for reviving his tariff agenda now appear severely limited.