This is where the right/left paradigm comes from. Debs was a complete Marxist nutjob that denounced religion yet gave speeches in a evangelical fashion. The only presidential candidate to recieve a percentage of the vote from behind bars. He had nothing to do with the progressive movement but rather wanted to nationalize industry.
When leftist call themselves "Progressive" and use Progressive phrases its pure propaganda. They are trying to take credit for Republican Teddy Roosevelts movement the Marxist Left actually ran against.