> Surely there's a mechanism through the courts for someone to challenge illegal tariffs
What you're describing is the Marbury tail wagging the Article II dog. The focus of the Constitution is allocation of power. The focus isn't creating a system where courts micromanage how the other two branches of government exercise that power. Marbury therefore goes to great lengths to draw lines between an executive's "ministerial" actions, which courts can supervise, and those that involve "discretion," which courts cannot. Marbury thus says:
> [W]here the heads of departments are the political or confidential agents of the Executive, merely to execute the will of the President, or rather to act in cases in which the Executive possesses a constitutional or legal discretion, nothing can be more perfectly clear than that their acts are only politically examinable. But where a specific duty is assigned by law, and individual rights depend upon the performance of that duty, it seems equally clear that the individual who considers himself injured has a right to resort to the laws of his country for a remedy.
The Tariff Act provision here is a classic example of something that Congress has entrusted to the President's discretion. The statute says: "Whenever the President shall find as a fact that any foreign country places any burden or disadvantage upon the commerce of the United States by any of the unequal impositions or discriminations aforesaid..."
Insofar as the courts can properly review such actions, their rule is to determine whether the prerequisites for invoking the authority have been satisfied--namely, did the President make a finding? Here, the President did make a finding. At that point, the courts' jurisdiction gives way to the President's discretion. The courts don't get to decide whether the President's finding is correct, or even whether it makes sense. At that point, the act is "only politically examinable."