The US Socialist Party as it existed from about 1900 to about 1920 was much more radical and Marxist in nature than the European socialist parties were. Compared to the third parties that exist today, the Socialist Party was pretty successful; for example, in the 1920 election the Socialist candidate Eugene V. Debs was in prison for violating the Sedition Act, but he still got about 1,000,000 votes, which was about 5% of the vote, I think. I'd like to see Nader or Badnarik do that well while incarcerated.

There I must defer to you on your knowledge of US history. The only bit I did in school was The Great Depression. :) British system.

It depends which European socialist parties you're talking about Ron. Parties that actually got into government either started out as, or in the case of parties like the SPD, became less radical; but we had and have radical, marxist parties capable of getting 5% or more of the vote. At the same time the Labour party was growing; the Communist party got two seats in Parliament over here. Look around Europe today, and we still have radical minor parties capable of winning seats in various parliaments (the PCF, the Left Party, Communist Refoundation etc. etc.)