Vermont Sen. Bernie Sanders, running in the Democratic presidential primaries, has raised about $15 million, his campaign said Thursday.

His campaign emphasized the grass-roots strength of his fundraising: 250,000 donors making nearly 400,000 contributions of $250 or less.

The numbers come from a quarterly disclosure report being filed at the Federal Election Commission, and are measured from when Sanders launched his campaign April 30.

The maximum legal contribution to a presidential candidate is $2,700. The Sanders campaign said its average contribution was $33.51.

The campaign said supporters gave "almost entirely with online donations."

Reliance on small donors cuts both ways. They provide a candidate with a ready-made network and grass-roots credibility — but it would take 80 donors giving that average $33.51 contribution to match one wealthier donor writing a check for $2,700.

The fundraising announcement came the morning after Sanders drew 10,000 supporters to a rally in Madison, Wis. — a signal that Sanders has drawing power among the liberal faithful.

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