Key issue is whether 1977 law allows for tariffs

Asked why no other president had used IEEPA to impose tariffs in trade disputes and other economic emergencies, he said tariffs were not the “natural tool” to address those problems.

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For instance, he said, tariffs would not have made sense to deal with the Iranian hostage crisis under former president Jimmy Carter.

Opponents say IEEPA does not specifically mention tariffs. And that the tariffs are a form of tax and the US Constitution vests the Congress - not the president ~ with the power to raise revenue and to regulate trade with other nations.

They also say the president can sanction individuals and nations, but not levy tariffs - that amount to taxes — on them.

Additionally, Congress cannot just hand over its broad constitutional responsibility to the president.

The case tests what is called “major questions doctrine”, which says the president cannot impose a broad policy with significant consequences on society and the economy unless Congress passes a law that specifically allows for it.

The Supreme Court had invoked that doctrine when blocking former president Joe Biden’s attempt to forgive billions of dollars in student loan debt.

Mr Sauer said the tariffs had helped Mr Trump reach consequential trade deals to help the US economy. The “major questions doctrine” does not apply when a statute concerns the president’s constitutional authority over foreign affairs and national security, he argued.