If the Supreme Court finds that the tariffs are, at bottom, a kind of tax, it is likely to rule against them, since the Constitution gives Congress, not the president, the power to tax. If the justices agree that the tariffs are diplomatic tools, they may sustain them, as part of the president’s foreign policy prerogative.

But the disconnect at Wednesday’s argument was more complicated than in the earlier cases because, in an unusual move, the introduction to the government’s main brief quoted and so adopted some of Mr. Trump’s public statements.

“One year ago,” the brief said, quoting Mr. Trump, “the United States was a dead country, and now, because of the trillions of dollars being paid by countries that have so badly abused us, America is a strong, financially viable and respected country.” and “the economic consequences would be ruinous” were the court to require the administration to unwind its tariffs deals.

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“In effect,” he said, “the government brief opened the door to considering the president’s statements by including them in the briefing, and that may enable the court to consider the president’s remarks when it would normally be very reluctant to do so.”