"Watch the courts" was the whispered message a well-connected diplomat told me in Washington DC last month, amid the previous episode of US tariff chaos.
Most eyes were on the high-profile case in California from the Democratic Governor Gavin Newsom – that President Donald Trump's trade tariffs were illegal.
In the event, it was a separate case at the International Trade Court filed by a dozen other states and some small businesses that have pulled the rug from underneath Trump's signature policy. (Tariffs imposed by the Trump administration that were struck down by the trade court on Wednesday will remain in place while the case makes its way through the courts.)
It raises the real question about whether the wider so-called reciprocal tariffs due in July will ever come in to effect, whether the 10% universal tariff can stick, whether nations will bother to negotiate, whether Congress will come to the president's rescue, and of course, the eventual reaction of the Supreme Court.
Much of this can be traced back to the highly unusual dynamic underpinning the Trump's tariff actions.
The very sight of the president proclaiming sweeping tariff rates on a variety of countries, culminating in his now infamous Rose Garden moment with the blue board, is the foundational legal problem here.
Typically, indeed constitutionally, trade policy is the domain of the US Congress. The chairs of the trade committees of the House and Senate (branches of the Ways and Means Committee) are very powerful positions.
President Trump bypassed all of that by proclaiming a variety of national emergencies. While he has some scope to act in actual emergencies, these cases contend that the sweeping use of these powers to announce permanent tariff changes was illegal and unconstitutional.
There is a fascinating assessment of the separation of powers in the US that includes reference to both former President Richard Nixon's limited use of the same powers and the Federalist Papers of Hamilton and Madison.
