1. I have been to Europe. I doubt a real true blue Leftist would regard even European "Socialist" parties as truly pure.
2. I've read the Communist Manifesto with considerable care, and it says nothing whatsoever about democracy as a desirable political system. It was written during the Revolution of 1848, when for a moment it looked as if Germany was going to get some kind of an elected government, possibly even with democratic elections. Marx wrote about a great variety of topics, not including political systems. For the mature Marx, economic structure was all-important and political institutions simply reflect the will of whoever controls the modes of production.
2. I did not mean to suggest that the Democratic Party is Leftist - whatever that means. Everyone is free to define "Leftist" for themselves, so that it is not very useful concept. What I meant is this. On a lot of issues, as they exist in peoples' minds today, there is a "left" side and a "right" side. And to the extent the two parties differ, the Democrats are invariably on "left" side of every issue. The country is increasingly polarized. And Nader agrees with the Democrats whenever they differ from Republicans; he just thinks Democrats are too moderate.
Nader does think both parties go too far in supporting Israel. He has a point there, but for me that's not enough. They say he is likely to get about 30% of the Arab vote, which is heavily concentrated in two swing states, Michigan and Ohio. In 2000, the Arab-American vote went overwhelmingly for Bush. That seems unlikely to happen a second time, so Nader could be crucial in winning, once again, for GWM.