[Right_Wing_Madman]

Congress has the power to tax, while the President is in control of foreign relations. Separation of powers becomes problematic in that tariffs are both a tax and an aspect of foreign relations.

My guess is that the Supreme Court will declare the blanket 10% tariff across all countries as unconstitutional as a taxation power reserved only for Congress, but allow the President to keep all the country-specific tariffs in place (Canada, Mexico, China, etc.) as the executive's authority in foreign affairs.

[Skwor]

I’d take that as it would be a null ruling. Trump can easily re-assert the 10% specifically to each country.

[Rockingham]

That is one possibility, but the Court could find that Trump and Congress both have the power to impose a general tariff, with neither ordinarily able to negate the other’s exercise of its distinct constitutional power. The exception would be that Congress could use the power of the purse (annual appropriation bills) to forbid the executive from spending money to establish and enforce a general tariff.