Obama campaign says it surpasses 4 million donors

President Barack Obama's campaign says it has surpassed 4 million donors, a record for a presidential campaign.

The president's field director Jeremy Bird announced the total in an email to supporters Saturday night.

Obama's campaign has relied on small donors to boost its fundraising totals through the summer and fall. The campaign raised $181 million in September, its biggest haul of the cycle.

Republican Mitt Romney's campaign has not yet announced its September fundraising numbers.