U.S. President Donald Trump said a Supreme Court ruling against his tariff policy would be "devastating" for the United States.

Speaking to reporters at the Oval Office on Thursday, Trump expressed hope of winning the case, calling it one of the most important cases in U.S. history.

The U.S. president said that so much revolves around tariffs as a mechanism for national security, and that without them, his administration would not have been able to make "phenomenal deals" with the European Union, Japan or South Korea.

Trump also said the administration would have to develop a "game two plan."

The Supreme Court heard arguments earlier in the week on whether Trump has the legal authority to use the International Emergency Economic Powers Act to impose tariffs, and, if so, whether he can do so without congressional approval.

Though the top U.S. court could take until June 2026 to make its ruling, it is expected to decide sooner.