The Great Depression led to political instability in the United States to the extent that it spelled the end of the Hoover presidency and brought on the resurgence of the Democratic Party. While the crash in the economy was caused by many factors, the Hoover administration's seeming inability to prevent or stop the disaster meant that the president took a lot of the blame.
Furthermore, the ill-conceived Smoot-Hawley Tarrif did a lot to damage the confidence that many Americans had had in their elected representatives. The careers of many politicians, including the two the tariff is named after, never recovered. Then, the tax rate hikes in 1932—a time when few Americans could afford them—further upset confidence in politicians.
When Franklin Roosevelt ran on the platform of change in the election of 1932, he earned the votes of many who were fed up with a government that seemed incapable of pulling the country out of the Great Depression. Herbert Hoover had lost credibility and was easily defeated. This resulted in the first significant victory for the Democratic Party since before the Civil War.