I noticed you didn't get any responses in three days so I figured I might at least be able to point you in the right direction. I'm far from an expert, but Eugene V. Debs led a growing socialist movement in the United States in the early 20th Century. Debs ran for president quite a few times but never made it out of single-digit vote totals. The movement had more success at the state and local levels than federal. It is a fairly well-known topic in U.S history so I doubt you will have any trouble finding much to read about it.