The majority found that the Constitution “very clearly” gives Congress the power to impose taxes, which include tariffs.

Once again the authority to do something goes back to the do-nothings.

Other Options That said, even if that happens, the Trump administration has several other legal avenues they can pursue. As Deutsche Bank noted last month;

For instance, the sectoral tariffs (e.g. on steel and aluminum) aren’t covered by the court ruling, whilst another option would be to use Section 122 of the 1974 Trade Act, which permits temporary 15% tariffs for 150 days.

And Goldman:

This won’t be the end of tariffs… the administration will almost certainly roll out alternative legal frameworks. Net result is probably slightly fewer tariffs, materially more trade uncertainty, and some incremental deficit concerns. Net-net, that’s mildly supportive for equities and mildly negative for bonds… but largely priced for both.

Meanwhile, Trump called the ruling a 'disgrace,' and told governors at a White House breakfast that he has a 'backup plan' in mind, though no details on that.