A majority of US Supreme Court justices appeared deeply skeptical of the legality behind a swath of Donald Trump's tariffs, as they heard a landmark case on Wednesday that could uphold -- or upend -- the president's economic agenda.

Billions of dollars in customs revenue and a key lever in Trump's trade wars are at stake, as the conservative-dominated panel once again grappled with the Republican's attempts to expand presidential powers.

The high court's nine justices are considering Trump's use of emergency powers to impose so-called "reciprocal" tariffs on nearly every US trade partner, as well as levies targeting Mexico, Canada and China over their alleged roles in illicit drug flows.

Several conservative justices, along with the three liberals, questioned whether the International E

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