On April 30, 2018, President Trump signed Proclamation 9705, invoking his authority under Section 232 of the Trade Expansion Act of 1962 to impose a 25 percent tariff on most steel imports and a 10 percent tariff on aluminum imports. This national security rationale—that domestic steel and aluminum production capacity was essential to military readiness—became the legal mechanism for one of the most consequential trade interventions of the administration's first term. While a handful of countries including Canada, Mexico, and the European Union received temporary exemptions, the tariffs applied broadly to steel and aluminum products entering U.S. commerce from most trading partners.

The economic consequences were immediate and widespread. American manufacturers relying on imported steel and aluminum as inputs—from automotive suppliers to appliance makers to construction companies—faced significantly higher material costs that were often passed directly to consumers. A consumer purchasing a pickup truck, kitchen appliance, or aluminum window frame absorbed the cost increase. Simultaneously, trading partners including China, Canada, the European Union, and Mexico implemented retaliatory tariffs targeting American agricultural exports, steel products, and manufactured goods. Farmers in Iowa and Illinois saw soybean and corn prices decline as Chinese buyers shifted suppliers, while American workers in export-dependent industries faced reduced demand.

This proclamation established a precedent that would persist and expand throughout subsequent administrations. The continuation of the national emergency on trade deficits declared in 2026 and the temporary import surcharge on international payments issued in February 2026 directly build from the framework Proclamation 9705 created. Each successive action expanded executive tariff authority and reinforced the use of national security justifications for trade interventions. The suspension of duty-free de minimis treatment for imports, also implemented in February 2026, represents a further escalation of the protectionist architecture initiated by these steel and aluminum tariffs.

The tariffs faced legal challenges but largely withstood judicial scrutiny, with courts generally deferring to presidential authority under Section 232. However, Congress never formally authorized these tariffs through legislation, relying instead on emergency powers invoked by the executive branch.