Carson finished January with just over $4 million cash on hand. But if his campaign continues spending at its current rate and doesn't substantially increase its fundraising, it will be running on little more than fumes by the end of this month.

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During the month of January, Carson's campaign spent $6.2 million and raised $3.8 million.

By contrast, when Carson surging last year, the retired neurosurgeon raised $3.5 million in just the first week of September. He has raised $57 million to date — more hard dollars than any of his GOP rivals.

But while Carson briefly led the polls late last year, he has slipped dramatically after a series of foreign policy missteps and staffing overhauls.

Carson's campaign has been criticized for spending a lot of its money on consultants. The Carson method of fundraising relies heavily on direct mail, which is an expensive way to raise funds.