For months, President Trump and his top advisers described tariffs as an economic cure-all, one that would bring in revenue to pay down the national debt, offset tax cuts, support struggling farmers and even provide dividend checks to Americans.

But when the White House’s solicitor general, D. John Sauer, defended Mr. Trump’s expansive use of tariffs before the Supreme Court on Wednesday, he expressed a much different view. Despite all the public justifications of the tariffs, Mr. Sauer suggested that they were not really about the money at all.

“These are regulatory tariffs,” Mr. Sauer said. “They are not revenue-raising tariffs. The fact that they raise revenue is only incidental.”

In remarks at the White House on Thursday, Mr. Trump said that if the tariffs were deemed illegal it would be “devastating for our country,” and suggested that he was contemplating contingency plans. He warned that trillions of dollars of investments pledged by Japan, South Korea and the European Union would be at risk if he were unable to threaten them with tariffs.