Eighty six years ago, President Herbert Hoover signed into law the most protectionist tariff law in American history, the Smoot Hawley Tariff of 1930, over the strong opposition of hundreds of economists who signed newspaper ads opposing the cutoff of foreign trade in the early months of the Great Depression.
These economists warned that creating tariff walls would backfire on the US economy, but Hoover did not listen, and he paid the price of a much worsening depression, leading to his defeat in 1932 for reelection by Franklin D. Roosevelt
Hoover also pursued a foreign policy of isolationism, refusing to participate in the League of Nations, and issuing the Stimson Doctrine in 1932, named after the Secretary of State, Henry Stimson. This document declared the US refusal to recognize the aggression by Japan against Manchuria, part of China in 1931, but making clear that no military or other action would be taken against foreign aggression anywhere in the world.
Hoover continued to be an isolationist after the Presidency, and opposed US entrance into World War II until after the Japanese attack on Pearl Harbor in December, 1941.
Now, Republican Presidential nominee Donald Trump is taking similar stands on both protectionism and isolationism, a pivot from the modern tradition of the Republican Party, and considered by many to be a major mistake in both domestic and foreign policy.