WASHINGTON — President Donald Trump’s power to unilaterally impose far-reaching tariffs is before the Supreme Court on Wednesday in a pivotal test of executive power with trillion-dollar implications for the global economy.

The Republican administration is trying to defend the tariffs central to Trump’s economic agenda after lower courts ruled the emergency law he invoked doesn’t give him near-limitless power to set and change duties on imports.

The Constitution says Congress has the power to levy tariffs. But the Trump administration argues that in emergency situations the president can regulate importation taxes like tariffs. Trump has called the case one of the most important in the country’s history and said a ruling against him would be catastrophic for the economy.

The challengers

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