I’d be open to getting behind the Green Party if they were smarter about how to infiltrate the political system. Simply running a third-party presidential bid every four years isn’t the way to do that. They should be organizing to penetrate electoral politics at the municipal and county level (How many Green mayors, councilpersons, county commissioners are there?), which would build a foundation for strong state-level parties, in turn developing a foundation for viable congressional and presidential campaigns. Look at the original Republican Party: schoolhouse to White House in under a decade.
If the Green Party would begin to get it together now, we could maybe elect a Green president with strong congressional support in 20 years. But I doubt they will, and for this reason the best hope for actual progressive change in US politics is to fight for a progressive/Berniecrat bloc to gain traction within the Democratic Party.