When the Depression set in, Hoover was president. And as a classic conservative president he did not want the government to step in and intervene. Instead he wanted to give encouragement and helpful advise to those in those in need. This caused people that were deeply affected by it to hate him. Those who were homeless made little 'towns' out of cardboard and called them 'hoovevilles' after the president who they despised.
So Franklin Dealeno Roosevelt ran for president and he won in a landslide because he was an advocate of huge government intervention to help sitituations like that. Being a classic democrat in favor of huge government control of everything he emplemented many reform programs to help get the country out of the depression.