The Supreme Court yesterday struck down Trump’s IEEPA tariffs, holding that the statute’s authorization to “regulate… importation” doesn’t include the power to impose tariffs. The majority’s strongest argument is simple: every time Congress actually delegates tariff authority, it uses the word “duty,” caps the rate, sets a time limit, and requires procedural prerequisites. IEEPA has none of these.

The dissent pushes back with an intuitively appealing argument: IEEPA authorizes the President to prohibit imports entirely, so surely it authorizes the lesser action of merely taxing them. If Congress handed over the nuclear option, why would it withhold the conventional weapon? Indeed in his press conference Trump, in his rambling manner, made exactly this argument:

“I am allowed to cut off any and all trade…I can destroy the trade, I can destroy the country, I’m even allowed to impose a foreign country destroying embargo…I can do anything I want to do to them…I’m allowed to destroy the country, but I can’t charge a little fee.”

The argument is superficially appealing but it fails due to a standard result in principal-agent theory.

Congress wants the President to move fast in a real emergency, but it doesn’t want to hand over routine control of trade policy. The right delegation design is therefore a screening device: give the President authority he will exercise only when the situation is truly an emergency.

An import ban works as a screening device precisely because it is very disruptive. A ban creates immediate and substantial harm.  It is a “costly signal.” A President who invokes it is credibly saying: this is serious enough that I am willing to absorb a large cost. Tariffs, in contrast, are cheaper–especially to the President. Tariffs raise revenue, which offsets political pain. Tariff incidence is diffuse and easy to misattribute—prices creep, intermediaries take blame, consumers don’t observe the policy lever directly. Most importantly tariffs are adjustable, which makes them a weapon useful for bargaining, exemptions, and targeted favors. Tariffs under executive authority implicitly carry the message–I am the king; give me a gold bar and I will reduce your tariffs. Tariff flexibility is more politically appealing than a ban and thus a less credible signal of an emergency. The “lesser-included” argument gets the logic backwards. The asymmetry is the point.

Not surprisingly, the same structure appears in real emergency services. A fire chief may have the authority to close roads during an emergency but that doesn’t imply that the fire chief has the authority to impose road tolls. Road closure is costly and self-limiting — it disrupts traffic, generates immediate complaints, and the chief has every incentive to lift it as soon as possible. Tolls are cheap, adjustable, and once in place tend to persist; they generate revenue that can fund the agency and create constituencies for their continuation. Nobody thinks granting a fire chief emergency closure authority implicitly grants them taxing authority, even if the latter is a lesser authority. The closure and toll instruments have completely different political economy properties despite operating on the same roads.

The majority reaches the right conclusion by noting that tariffs are a tax over which Congress, not the President, has authority. That is constitutionally correct but the deeper question is why the Framers lodged the taxing power in Congress — and the answer is political economy. Revenue instruments are especially easy for an executive to exploit because they can be targeted. The constitutional rule exists to solve that incentive problem.

Once you see that, the dissent’s “greater includes the lesser” inference collapses on its own terms. A principal can rationally authorize am agent to take a dramatic emergency action while withholding the cheaper, revenue-lever not despite the fact that it seems milder, but because of it. The blunt instrument is self-limiting. The revenue instrument is not. That asymmetry is what the Constitution’s categorical division of powers preserves — and what an open-ended emergency delegation would destroy.