Money Can't Buy Everything
John Sides uses Meg Whitman to talk about self-financed candidates. This could be applied to Mitt Romney:
[I]t is important to remember that many candidates spend their own money because they are forced to, not because they necessarily want to. That is, they invest their money because they are facing strong opposition and could easily be defeated, or because they are languishing in the polls and desperately need to give their campaign a jolt, or because they are uncertain about their ability to raise money. Self-financing may be as much a sign of weakness as as sign of strength.
Second, dollars raised from other donors appear to produce more votes than dollars provided by the candidate. This may reflect the additional benefits of cultivating a network of supportive donors.