Why did President Hoover's response to the Great Depression fail?
It was based on Protectionism
Hoover's response to the Great Depression was the Smoot-Hawley tariff which rose tariffs on over 20,000 products. This measure led to retaliation from foreign countries especially from Europe and they rose their own tariffs on their American imports, the American economy was hit back and it explains why Hoover's policy failed.
Hoover was nicknamed "Do nothing" by the Democrats, they blamed him for sticking to Laissez faire economics, but this accusation was wrong as he pushed for more state intervention which eventually failed.