For the steel and aluminum tariffs, Mr. Trump is using what is known as Section 232 of a 1962 trade law, which allows for import barriers to protect national security. Curtail the administration’s negotiating abilityTo conduct negotiations on overhauling the North American Free Trade Agreement, Mr. Trump is relying on a law known as fast track, or trade promotion authority. Such a move could also box Mr. Trump in, making him more likely to follow through on threats to withdraw from Nafta. If such funding changes came in a broad spending bill, Mr. Trump would have a hard time vetoing it. Still, Mr. Trump was elected president with a clear platform on trade, and in some districts publicly clashing with the president could hurt lawmakers’ re-election campaigns.

Source: Wall Street Journal March 09, 2018 10:30 UTC