So, Hillary supporters who were anti-Bernie and now some Bernie supporters have been pushing this anti-3rd party notion (that a vote for Jill Stein is a vote for Donald Trump) because Ralph Nader ran in Florida (not that Ralph's run was the reason the Supreme Court anointed George W. Bush).Well, if Ross Perot hadn't run in 1992, would Bill Clinton have won? I doubt it. More importantly, was Bill Clinton really better for the nation than a George H.W. Bush second term would have been. Bill made some really big mistakes that Bush-41 wouldn't have (not that George I wouldn't have continued making plenty of his own).
The biggest issue, however, is whether this time is comparable to any prior election. I don't think it is. I think the Internet has changed everything and when coupled with the impacts of war and the Great Recession, this generation is primed to way outdo the New Deal of FDR.
The counter will be that we can't take any chances because of Trump. Look, if Trump is elected, he'll make mistakes, but he won't be more of an existential threat than Hillary Clinton would be. She's a huge war-hawk (Trump is no pacifist, but he's no war-hawk) who's caused massive damage around the world with her terrible advice Barack Obama foolishly took (and he knows it, having said Libya was his greatest error).
Don't go along with anti-3rd-party hysteria.