In February, the Supreme Court of the United States told the President he could not impose tariffs the way he had been imposing them. The vote was six justices against three. The ruling was obeyed the same day: the tariffs were switched off, and importers are owed refunds that could reach a hundred and seventy billion dollars.

This Monday, the same kind of tariffs came back, at fifty percent — double the rate the struck-down ones had reached. Nobody defied the court. Nobody ignored the ruling. The tariffs were issued under a different law: one that has been sitting on the shelf, unused, for ninety-six years.

On Monday the twentieth of July, the President signed three proclamations placing fifty percent tariffs on Canadian goods — one covering motor vehicles, one alcohol, one dairy. Between them they reach a long list of products, from wine to hockey sticks to cement. Energy, fish and critical minerals are among the exemptions. The tariffs take effect on the nineteenth of August, and they apply to goods the North American trade agreement normally covers.

The legal basis is Section 338 of the Tariff Act of 1930, one of the oldest trade laws still on the books. It lets a president add duties of up to fifty percent on any country he determines is discriminating against American commerce — and it only requires that the President "find as a fact" that discrimination exists. No investigation is required. Until Monday, no president had ever used it to actually impose a tariff.

Follow a single piston. It is cast in one country, machined in another, sent north for assembly with its rings and rods, shipped to yet another plant, and finally dropped into an engine that crosses the border one more time to be fitted into a car. That is six international crossings for a single component — and that is normal. Canada's prime minister says the average car part crosses about six times; industry estimates run to eight. Roughly three quarters of everything Canada sells abroad goes to the United States.

None of that was built for a world of thirty-day notice. A factory line is an investment measured in decades. And on the first of July, the United States, Canada and Mexico met for the trade agreement's scheduled six-year review, where the United States declined to extend it. The agreement survives, but instead of being locked in for another sixteen years, it now comes up for review every single year.

Under the American constitution, tariffs belong to Congress. Article One is explicit: Congress shall have the power to lay and collect duties. It does not say the President.

But over ninety years, Congress handed pieces of that power to the executive branch, one law at a time, and each had a reason that seemed sensible on the day it passed. The oldest is from 1930 — Section 338, the one used this week — for responding to countries that treat American goods unfairly. In 1962 came a second, for national security. In 1974, two more in a single year: one for a sudden crisis in the country's finances, one for unfair trading practices abroad. In 1977, a fifth, for genuine national emergencies.

Any one of them is defensible on its own; a legislature of 535 people is not built for speed. But together they are five different legal doors into the same room — and because these powers were handed over permanently, none of them expires on its own. A law that is never used never goes away. It just gathers dust, waiting.

The tariffs the President had imposed across dozens of countries were built on the 1977 emergency law. Importers sued, and in February the Supreme Court ruled against the government, six to three. Chief Justice Roberts wrote that the emergency law "contains no reference to tariffs or duties," and that until now, no president had read it that way. The government lost the case, and the tariffs were switched off that same day.

And on the same day, a different law was used: the 1974 law for a sudden crisis in the country's finances, allowing a temporary extra charge on imports from every country at once. That one has a limit — fifteen percent maximum, and a hard stop after a hundred and fifty days, after which Congress has to vote. Those days run out on the twenty-fourth of July. The new tariffs were signed on the twentieth, under the law from 1930. Whatever the reasoning behind the timing, the structure made that handover available: when one authority runs out, another one is already there.

Section 338 requires that finding of discrimination. Where does it come from? From Canada's own measures — a twenty-five percent duty on certain American vehicles since April 2025, and the decision by almost every Canadian province to stop buying and selling American alcohol.

But those measures were themselves a response to earlier American tariffs, which were themselves argued as an answer to conditions the American side considered unfair. Trace it back far enough and there is no clean first move, which is exactly what makes this a loop rather than a line. Ontario's premier has called for matching new tariffs "dollar for dollar"; Canada's prime minister says his government believes in free and fair trade and is ready to negotiate. Both are true at once — inside this structure, retaliating and negotiating are not opposites.

Look again at that 1974 law, the one used in February. Alone among the five, it has a fuse: the tariffs it allows are capped at fifteen percent, they expire automatically after a hundred and fifty days, and to continue them Congress has to act. The power goes back to its owner unless somebody deliberately renews it. And you can watch that design working — that fuse burns out this week, which is why the question of what comes next arose this month at all.

The honest cost is real. A hundred and fifty days of tariffs still happen, and a fifteen percent ceiling gives a negotiator less to push with, because the other side knows exactly how high it can go and exactly when it ends. A fuse slows the power down. It does not stop it. But it is the only one of the five that hands the power back by itself.

The second redesign is to remove the shelf entirely — roughly what the European Union did, though not on purpose. In the EU, trade policy is not a national power at all. It belongs to the Union: the European Commission negotiates, but agreements need approval from the member governments and from the European Parliament, and the EU's court enforces the result. And European law sits above the law of any single member country, so a national government cannot cancel a trade agreement with a decision of its own. There is no national door to reach for.

The cost is exactly what it sounds like. It is slow, because twenty-seven governments have to agree. And an individual country gives up the ability to defend itself quickly, including in the cases where moving fast would have been the right call. That is a real handover of national control.

The third redesign is the most direct: take the shelf apart. One narrow version already exists as a bill, introduced in 2025 by Democratic members of the House Ways and Means Committee, which would strike Section 338 from the law entirely on the grounds that a power from 1930 that no president had used in ninety years should not remain available. It has not passed. Proposals to put time limits on handed-over powers have come from both parties over the years, and none of those has passed either.

The broader version is a design principle: give every one of these handed-over powers an expiry date. Not a review, and not a report — the power would simply switch itself off, so that keeping it alive requires the legislature to vote again, the way some war powers and security laws already work. The costs are real too. A legislature that must vote is slower than a crisis, and sometimes a country genuinely needs to move in days. And renewals tend to become routine, so the fuse quietly turns into a formality.

The court did its job. It read one law, decided that law did not authorise what was being done with it, and said so. That ruling stands, and the tariffs it struck down are gone. What the ruling could not do is reduce the total amount of power on the other side of the wall, because a court can only answer the question in front of it: does this particular law permit this particular action? When other laws are available, a ruling of no does not stop the action. It just sends it to a different door.

The shelf belongs to Congress. It was built by Congress, one reasonable decision at a time, across dozens of administrations of both parties. It is the only body that can take it apart, and it has never had a deadline forcing it to look. Three doors on that wall are still shut. None of them is locked.