But despite being far outpaced by his Republican counterparts, Burton remained optimistic that his group could raise $100 million by November to support the president's campaign. And Burton said he thought Priorities USA had an advantage in spending money wisely.

“I think even more important than the number of what we're going to raise and spend is how we spend it. If you look at what we've done over the course of the last six or seven weeks, we've spent $10 million, $10 million talking about Mitt Romney's career in business. It's one of the only things that's actually moved numbers in this race," Burton said. "You look at any public poll, any private poll, the focus groups, they all say that. What was supposed to be Mitt Romney's biggest asset, his experience in business, has actually become one of his biggest liabilities.”

Burton also said the group had received a "couple" of multi-million dollar donations, including $2 million from Qualcomm founder Irwin Jacobs.

“It's a wide range of folks, from our friends in San Diego and the entertainment community to Chicago to New York. There's a wide range of people," Burton said.