Greatest President we never had

[Peter the Lefty]

I was originally planning to make this a poll, but it would've been way too complicated to have every single person whose ever run for president but failed to win, as well as everyone whose ever been hyped as a potential candidate but never run.  So, I just put it as a topic.  Who is the greatest president the US has never had?

(For me, it'd be Eugene V. Debs, but Robert La Follette, Henry A. Wallace, and Frank Zeidler would also be up there.)

[Peter the Lefty]

I don't think Ralph Nadar is among them, but I'm a bit surprised he hasn't been mentioned.  I'd also put Bernie Sanders there since it's clear he'll never run.  I would also be tempted to put Kucinich as one were it not for his recently-revealed contacts with the Gaddafi regime.