Forget about aspirations and consider their odds of winning. Not a single 3rd party candidate in history had a real chance of winning the Electoral vote, not one. In the handful of races where a 3rd part candidate got a significant percentage of the popular vote; they ended up splitting the vote for the main party they were most like, allowing the remaining candidate to win. AKA, spoiler.
Bobby is a smart man, he knows he has no chance of winning, so he's in it for an ulterior motive. Whether it's to sound the alarm on how radical the Democratic Party has become, draw attention to his anti-vax position, to help Trump win, or something else; he's there for some other reason than winning.
As to your question, there's no way to know for sure, but Ralph Nader and Ross Perot have both been accused of being in the race only as a spoiler. Ross Perot had a weird hatred for Bush.