In the years between WW 1 and the Great Depression, the socialist party (sometimes also labeled the progressive but this is generally incorrect) in the United States made strong inroads. They had become active in the industrial (mining and rail) strikes of the late 1890's, the farmer's revolts and the Grange movement. Teddy Roosevelt in the 1912 election has witnessed a hostile and bitter election as the three groups struggled for power. Some historians consider it a close call.
In the 1920's, they won increasing numbers of elections, gaining supporters from all walks of life. The 2-party platform of the Democrat and Republican was in severe danger from the growing strength of the Socialist Party and its candidate Eugene V. Debs. Although, the group was not as vigorous as in the previous decade, there were enough unsettled voters that it was growing issue. It was so worrisome that FDR actually began to integrate many of the ideas and suggestions from the Socialist Party platform into the his own campaign and the campaign of the whole Democratic Party. The jobs acts, social security, and other activities of FDR's "New Deal" reforms were all initally (to some degree) part of the platform of the American Socialist Party. In essence, he grafted into the Democratic Party the values and goals of the Socialist movement. It worked, in the end he was able to attract enough Socialist votes to carry the day and the Socialist Party was a minimal independent political power for many years after that.
Forced underground in the 1950's and the era of McCartheyism, the party begant to reassert itself in the late 1960's and since the 1980's have run a Presidential candidate almost every term.
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