The Huffington Post has learned from sources close to both candidates that the Obama campaign will surpass the Clinton campaign in second quarter fundraising. "It's a matter of pure mathematics," an Obama fundraiser told HuffPost. "We had 104,000 donors in the first quarter; Clinton had 60,000. And while 75 percent of Hillary's contributors had maxed out, only 50 percent of ours had. So we had had a lot more potential to grow -- and we did." The fundraising period for this quarter ends on June 30, and campaigns have until July 15 to disclose their numbers. "Even though there are over three weeks left," a Clinton source told HuffPost, "it will be next to impossible for us to make up the difference. The machine we have at the $2,300 level is a superior machine, but the Obama campaign continues to beat us with small donors and on the Internet."