Vermont Sen. Bernie Sanders' presidential campaign says it has raised $15 million since launching his bid in late April.

The campaign has received money from about 250,000 donors.

Sanders' campaign is releasing preliminary totals for the fundraising period that ended this week. He trails Hillary Rodham Clinton in fundraising by wide margins -- Clinton's campaign says it has raised $45 million since mid-April.

But Sanders has been drawing large crowds at his rallies and appeals to many Democrats. His campaign says the average donation is $33.51.

Sanders is aggressively courting the most liberal grassroots voters by running largely on a platform of reducing income inequality. His stock has risen in early states like New Hampshire and Iowa, but he still trails Clinton in early polling.