On March 22, 2018, President Trump signed Proclamation 9705, invoking the rarely used Section 232 of the Trade Expansion Act of 1962 to impose a 25 percent tariff on imported steel and a 10 percent tariff on imported aluminum. The legal mechanism allowed the president to implement these duties without congressional approval, bypassing traditional trade legislation processes. While certain countries including Canada, Mexico, Australia, and South Korea received temporary exemptions through subsequent negotiations, most nations exporting these metals to the United States faced immediate tariff exposure.

The tariffs rippled across the American economy with tangible consequences for manufacturers and consumers. Steel importers and domestic producers faced immediate price increases that cascaded through supply chains. Automakers, appliance manufacturers, construction companies, and packaging producers—all dependent on affordable steel and aluminum inputs—confronted higher production costs. These increased expenses ultimately transferred to consumers through elevated prices for vehicles, household appliances, building materials, and countless other products incorporating these metals. Small manufacturers without the scale to negotiate long-term fixed-price contracts absorbed disproportionate cost increases.

This action established a template that would define subsequent trade policy. The assertion of national security as justification for trade barriers set precedent for the Continuation of National Emergency on Trade Deficits declared in 2026, which similarly maintains tariff authority through emergency powers. The steel and aluminum tariffs also preceded the 2026 Temporary Import Surcharge and the suspension of duty-free de minimis treatment for all countries, indicating an escalating pattern of protective trade measures. Each successive action built upon the legal and political ground established by these initial proclamations.

The tariffs faced immediate opposition from affected industries and trading partners. Numerous countries initiated retaliatory tariffs against American exports, particularly targeting agricultural products from key political constituencies. Some manufacturers challenged the Section 232 rationale in federal court, arguing the national security justification was pretextual. However, courts proved reluctant to second-guess presidential determinations under Section 232, and no successful legal challenge eliminated the tariffs' core provisions.

Reversing these tariffs would require either congressional action to limit Section 232 authority or presidential proclamation eliminating them. The tariffs' persistence through 2026 demonstrates their entrenched status in American trade policy, despite their initial economic costs to manufacturers and consumers.