You don't quit because you happen to be behind. You want to see how you do. And who knows? Maybe somebody will stumble.
I like Mitt Romney as a person. I think he's a dignified person. But I have no common ground on economics. He doesn't worry about the Federal Reserve. He doesn't worry about foreign policy. He doesn't talk about civil liberties so I would have a hard time to expect him to ever invite me to campaign with him.