1)Think about Bill's financial situation and how much it costs him to run a good campaign. Budget often is a very important factor in campaigns. Think about third parties as a comparison. How much do they have? Can you say "Ross Perot"?. He only did so well in the election because he was filthy rich( he spent 65.4 million USD on his campaign, and the money came out of his own pocket). I doubt Bill is that rich.
2) Think about his name. How well-known is he? Is he like Arnold who has never been in politics before (Max, don't beat me up!), but is famous? Incumbents tend to win election due to their name and budget
3) Coming soon, I'm thinking about it. But think of image right now.