Final answer:
Hoover's initial response to the Depression that worsened the downturn was the Smoot-Hawley Tariff. It raised tariffs on imports, leading to retaliation and a decline in international trade.
Step-by-step explanation:
Hoover's initial response to the Depression that most economists believe worsened the downturn was the Smoot-Hawley Tariff. This law, signed into law by President Hoover in 1930, raised tariffs on thousands of imports, leading to retaliation from foreign trade partners and a decline in international trade. The tariff led to a further worsening of the global depression. Hoover also attempted other measures, such as the creation of the Reconstruction Finance Corporation (RFC) and the Emergency Relief Act, but these were insufficient to address the economic crisis.