[quote=@Vilageidiotx]

They can't win, but a third party stealing significant chunks of the vote is the sort of thing party analysts pay attention to. 
[/quote]

Is it, though? I'd bet that a majority of American voters wouldn't recognize the name Ross Perot, and he had an order of magnitude more support than the Greens and Libertarians combined. Free trade is also still supported by all mainstream candidates in both parties.