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Actually, historically it can be shown that it is the extremes of the party that drive and determine the political debate and have far more influence on actual policy than the candidates who win. So voting for Kucinich is not crazy, but rather one of the most relevant things you can do.
This is one of the basic misunderstandings of most voters about the strategic significance of their vote. Issues like environmentalism, social security, medicare, pensions, workers compensation, all started as third party issues and in the case of the latter four as the issues of a perennial socialist candidate for president, Eugene V. Debs, in the early part of the 20th century. (FDR eventually stole his platform and enacted all his ideas.)
The third party positions or extremes within one of the major parties introduce ideas which the mainstream candidates eventually appropriate and which then become policy. The major candidates rarely have any ideas that are their own.
This is how the religious right, a small minority in the Republican party, came to be so powerful. They voted for the extreme and were willing to see Republicans lose elections. Eventually the Republican party moved to the right and took the Democratic party with it.
In the long run, voting for Kucinich has the most strategic potential power. The more people support his points of view, even if he loses, the more other candidates will adopt his ideas and the more they have the potential to become actual policy. Democrats always make the mistake of looking at the short run, thinking of how they can win now, and the long run result is the disjunction between Democratic values and Democratic candidates that Traister describes. (And the Democratic candidates often still don't win.)
The policies that get adopted as law have little to do with who actually wins elections. Politics is not about who wins, but voters (especially Democrats) don't get this.