Trump’s 10% tariff expires July 24—and the uncertainty premium is coming back. The last five months were not normalization; they were a 150-day pause. Markets are watching whether the average tariff rate eventually climbs from roughly 11% to 17%, but that is only the first-order risk. The larger problem is the return of a corporate rulebook that cannot be trusted. The legal route changed The Supreme Court struck down most of Trump’s second-term tariff regime in February, holding that the emergency law used by the administration did not authorize tariffs. Trump bridged the gap with a 10% surcharge under Section 122, giving businesses five months with at least one number they could model. Now the administration is expected to rebuild the regime through Section 301, which requires more process but can support tariffs that remain in place indefinitely. USTR has already proposed rates of 10% or 12.5% across 60 economies through its forced-labor investigations, with the potential package covering 99% of U.S. trade. The final structure still depends on USTR’s report, implementation guidance and decisions on more than 1,500 company comments seeking relief. That is where the market risk starts. Uncertainty is the hidden tariff A fixed duty is a margin assumption. A changing framework is a capital-allocation problem. Management teams can respond to a known tariff by raising prices, switching suppliers, absorbing costs or redesigning products. They cannot confidently underwrite a factory, long-term sourcing agreement or multi-year margin target when country rates, exemptions and legal authorities can change within a quarter. That uncertainty hits before the tariff itself through inventory pull-forwards, shorter contracts, delayed capex, higher working capital and wider earnings guidance. You can hedge currencies, freight and some commodities. You cannot cleanly hedge a policy rulebook that gets rewritten mid-quarter. Import-heavy retailers and manufacturers remain the obvious exposure, but the damage is broader because lower planning confidence makes forward estimates less reliable across the supply chain. Stocks may initially shrug if the replacement tariffs land near the expiring 10% levy. That would be too narrow a read. The real risk is a stack of Section 301 actions, bilateral pressure and future investigations that repeatedly resets the assumptions behind earnings models. Bottom line: a stable 17% tariff regime would be costly but modelable, while an unpredictable one deserves a larger earnings discount and a lower multiple.