The Supreme Court never says in advance which cases it will rule on. We only know that one or more decisions will be issued today. There was a hearing in early November, and a ruling has been expected at the start of this year.
What is at stake here is the future of most of the tariffs imposed by Donald Trump. In November, a few days before the hearing at the Supreme Court, we explained the case in detail.
During that hearing, the justices were skeptical of the US administration's arguments. That is why observers believe the likelihood of the Supreme Court striking the tariffs down is quite high.
While that prospect would have delighted markets a few months ago, it is likely Wall Street would now side instead with Donald Trump. "If the Supreme Court rules against the United States of America on this national security windfall, WE'RE SCREWED,” the US president wrote earlier this week.
Moving on
If investors are not quite in Donald Trump's frame of mind, there are nevertheless several factors suggesting that everyone would be satisfied with a Supreme Court decision favorable to the US administration.
First, nobody wants the tariff issue to dominate our days again. What markets hated last year was the uncertainty generated by this saga. The threats, the announcements, the deadlines… If 2025 ended with average tariff levels at their highest in a century, at least they were set and allowed companies to organize.
If the Supreme Court were to invalidate the tariffs, we would, in a way, get a season 2 of this saga. Because Donald Trump can reimpose them under other laws: Section 232 of the Trade Expansion Act of 1962, Sections 122 and 301 of the Trade Act of 1974, Section 338 of the Trade Act of 1930…
Tariffs are the key element of economic policy; there is no reason to expect him to give them up. And beyond that, they are his favorite weapon. In recent hours, Donald Trump has threatened every country trading with Iran with additional 25% tariffs.
Filling the deficit
Then there is the issue of refunds. In theory, if the tariffs are illegal, everything collected by the US government must be returned to companies. One can imagine the administrative chaos that would create.
It is also a factor that could weigh on the bond market. About $133.5bn is at stake in the Supreme Court decision, according to the latest tally from US Customs. Long-term yields could therefore rise if the tariffs are invalidated, which is generally a headwind for equity markets.
It is interesting to note the complete reversal in perspective from the bond market's point of view. Last spring, tariffs had pushed yields higher, as investors played the sell America trade (they sold US stocks, the dollar and Treasuries). Donald Trump himself had paused the reciprocal tariffs to calm the bond market.
But over time, tariffs have become a source of revenue that slightly cushions the US deficit. In FY 2025, the deficit came in at $1,670bn. Yes, it is still huge, but it is the lowest figure in three years, and tariffs largely explain that reduction.
A constitutional crisis?
Since the start of his second term, Donald Trump has done everything to push the limits of presidential power. He has repeatedly defied the courts and has completely encroached on Congress's prerogatives.
So far, the Supreme Court has not really opposed him. The question everyone is asking is whether he could decide to ignore a decision by the highest US court, which would then amount to a constitutional crisis.
This scenario is being considered because the Supreme Court has no independent means of enforcing its decisions. Responsibility for proper enforcement rests with the executive branch-and therefore with the president of the United States first and foremost.
In US history, there is a precedent in which a president did not comply with a Supreme Court decision. It was President Andrew Jackson in 1832. He then defied the Chief Justice with this now-famous line: "John Marshall has made his decision; now let him enforce it.”
