Just another note on the Greens, prompted by this earlier post
The problem, really, is that the Greens are setting their sights too high. They should be moving into state and national Congresses, not the Presidency. One is irreversibly tied to the two-party system; the other is not, and is more tied into local politics that the Greens could exploit. The Greens should be pouring their resources into challenging Democrats for more liberal congressional seats, and then making deals with the Dems to coordinate policymaking in Washington and in state capitols. They could build their influence and have a realistic shot at influencing policy. Yes, it means that the Greens wouldn't really have a shot at the presidency for about a decade or two, but that's the reality of the project- successful "invasion from the margin" is a very slow process.
Of course, this presumes that Green voters, activists, and politicians are actually interested in policymaking, and from that I think they "purity is the enemy of goodness" attack on the Greens may have some merit. I think the Greens think of themselves as a social movement, and social movements are near-sacrosanct within much of the left. Fine, they have their purpose, but successful social change requires a "grassroots and treetops" approach; you need a governmental branch as well as broad social movements. Even the IRA understood this, and they were far more extremist than the Greens would ever be.