On May 31, 2018, President Trump invoked Section 232 of the Trade Expansion Act of 1962—a Cold War-era statute designed to protect domestic industries deemed critical to national security—to impose a 25 percent tariff on imported steel and a 10 percent tariff on imported aluminum through Proclamation 10044. The tariffs took effect June 1, 2018, and applied broadly across most trading partners and product categories, though the administration negotiated exemptions for select countries over subsequent months. This legal mechanism, which grants the president considerable discretion to restrict imports without congressional approval, became the foundation for an expansive tariff program that extended well beyond steel and aluminum into automobiles, machinery, and consumer goods.

The practical impact fell heaviest on American manufacturers and consumers dependent on steel and aluminum inputs. Automakers faced immediate pressure as steel costs rose, ultimately trickling into vehicle prices for consumers. Construction companies encountered higher material costs for structural steel and aluminum components. Appliance manufacturers, packaging producers, and machinery makers all confronted supply chain disruptions and price increases. Small and mid-sized manufacturers, lacking the pricing power of large corporations, struggled disproportionately to absorb these costs while remaining competitive.

This tariff action marked the opening salvo in Trump's trade war strategy and established a pattern that would persist and escalate through subsequent years. The May 2018 proclamation preceded Section 301 tariffs on Chinese goods, agricultural tariffs, and automotive tariff threats. By 2026, the administration had institutionalized this approach, with the continuation of a national emergency on trade deficits in March that year enabling ongoing tariff authority, while the February 2026 suspension of duty-free de minimis treatment further tightened restrictions on imported goods entering American markets. The trajectory reveals a consistent doctrine: using national security and emergency authorities to justify protectionist measures that reshape the cost structure for domestic commerce and cross-border trade.

Legal challenges emerged but proved limited in scope. Courts largely deferred to executive authority under Section 232, treating national security determinations as largely unreviewable. Congress never mustered the political will to override the tariffs, despite bipartisan concern from manufacturers and retailers. Reversing these tariffs would require either presidential action, congressional legislation, or negotiated trade agreements restoring prior conditions—remedies that remain politically contentious and economically complex given years of supply chain adaptation.