Nader was just a potential spoiler, but Perot got 20% of the vote which is enough that someone doing only modestly better could win in a three way race.

A strong, credible candidate (which Nader wasn't) who has sufficient backing and resources (which Nader didn't), and doesn't screw up (as Perot did) absolutely could win. I don't see it happening this time around. For one thing, it is very late in the process to organize, gain recognition and support, and get ballot access. When Perot ran, he announced it in February. No one is doing that this year, and several of the possible candidates have ruled it out.