Where are these "good enough" third parties? In my (mostly but it's complicated) Democratic state, there have been third party candidates in various local positions, especially in urban areas, but it's been more a way to thumb their nose at Democrats rather than any political differences. I struggle to see how any left-leaning third-party would have much relevance in any of our bluish states and they are unlikely to get any traction in red states. If we want to talk about a third-party that looks like Eisenhower Republicans, now that might be interesting but thus far the right-wing of the country has shown little appetite.