(CNN) Former Vice President Joe Biden burned through his campaign donations at a blistering pace over the summer -- spending more than he took in and leaving himself just a fraction of the cash available to his better-funded rivals for the Democratic presidential nomination.

Biden's campaign entered October with $8.98 million remaining in its bank account, after spending more than $17.6 million during the July-to-September quarter.

Biden raised $15.7 million during the quarter, according to a report filed by his campaign on Tuesday, shortly after the conclusion of the fourth Democratic presidential debate.

The cash Biden has remaining a little more than three months before the Iowa caucuses puts him at a financial disadvantage to rivals such as Sen. Bernie Sanders of Vermont, who reported having more than $33 million stockpiled for the primary slog ahead.

Sanders relied on small-dollar donations for about 60% of his contributions over the summer -- giving him a pool of donors to tap repeatedly before they hit legal contribution limits.

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