In the case of Perot - it was Perot. His "candidacy" was for the sole purpose of disrupting Bush 1's re-election. After seeing to it that Bush wasn't re-elected, Perot proceeded to snipe at Clinton.
IMO, if you're going to be a party-pooper, don't snipe at the results.
BTW, when Dole ran, the opponent was Clinton and in that race I would agree, Dole shot himself in the foot. He ran a weak campaign
In other words, he is a self-promoter. As is Ralph Nader, etc. etc. etc.
My narrow point is that casting blame to others for not winning elections is responsibility-avoidance and counterproductive. Political parties are like businesses. If you want the most customers (and there -is- competetition) you need to tailor your product and marketing in order to win. If you don't win, it's your own fault, not the competition's fault.
I blame the GOP for losing to Clinton, twice.