I'm entirely in sympathy with the need for a third, progressive party in the U.S. But to nominate a presidential candidate before establishing a viable presence in the legislative branch is futile, and self-defeating. It is self-defeating because any non-credible detraction from a united front of left and left-of-center forces will only anger (even outrage) and alienate a majority of left and left-of-center voters. And the argument that there is no significant difference between the two established presidential candidates is not credible. I'm sorry, it's just not even arguable.
A viable third-party presidential candidate will only be achieved by first establishing a significant presence in the House of Representatives and state legislatures, and some presence in the Senate. And a significant progressive third-party presence in the legislatures will only be achieved by, initially at least, running candidates only against conservative Democrats, or against Democrats who are themselves recognized as having little chance of winning.
A third party that is recognized as being allied with progressive forces in the Democratic Party can eventually win over a sizable number of progressive Democrats. A party that is realistically viewed as nothing but a spoiler will never do so.
It is arguable that a third-party presidential candidate is necessary to focus attention on an alternative legislative agenda, and on the races of third-party legislative candidates. If so, a third-party presidential candidate should make it clear at the outset that he or she will release the party to the "lesser of two evils" if a viable campaign can't be established. It's the only way to become constructive and appealing, not destructive and antagonistic. It's the only way to eventually succeed.
Third-party progressives! Listen to the resounding voices of the vast majority of other progressives. Re-think what you are doing! Please, join a united front of progressives in 2008, for at least some short-term relief from the national self-destruction of the last eight years.