The Supreme Court is exposing President Donald Trump's secret behind tariffs — and who they actually end up "handicapping."

In a conversation with Dahlia Lithwick and Mark Joseph Stern for Slate's Amicus podcast, Marc Busch, the Karl F. Landegger Professor of International Business Diplomacy at the Edmund A. Walsh School of Foreign Service at Georgetown University, describes what the president's tariffs actually mean and how the Supreme Court is interpreting them.

"This case is so much bigger than trade," Busch said. "This is a separation of powers case, and it deserves to be taken very seriously precisely because of that. But there are some basics in economics that would have shed more light on what a power grab this is with respect to wanting a means of raising revenue."

Trump has never laid out the argument for why tariffs benefit Americans or what his strategy is behind them, Busch explains. And last week, it was clear that the tariffs were not just about retaliation over foreign countries and longtime trade partners, including Mexico, Canada and China.

"I was elated to hear that line of questioning, perhaps best articulated by Justice Sonia Sotomayor. What a relief to hear them utter that line: 'Tariffs are taxes,'” he adds.

"There’s no way to misunderstand these as anything other than what they are, which is as a tax that disproportionately hurts American manufacturers," Busch said. "You have to keep in mind about half of what the U.S. imports includes intermediate inputs, which are then used for production, including to export. So this manufacturing renaissance that the administration likes to dangle in front of us is far-fetched because we’re handicapping precisely those that we wish to champion."

Trump has argued that he has the power to issue tariffs under the International Emergency Economic Powers Act of 1977, which gives the president powers to regulate transactions involving any property that a foreign country has interest in to handle an unusual or extraordinary threat.

The question of power is one that came to the surface, he argued.

"The one thing I haven’t heard in the media played up nearly enough was the logical conclusion of Solicitor General John Sauer’s argument. He said in defense of his spin that this is a foreign-facing tariff, not a revenue-generating tariff, that in the president’s ideal state of the world, there is no revenue collected. Why? Because every business has moved to the United States and is sourcing and doing everything domestically such that the tariff wall is irrelevant and not a revenue-raising mechanism," Busch said.