One of Obama's top fundraisers, whose name was not reported, told The New York Times they were worried Obama spent too much too soon on his campaign.
"There is a lot of worry that Romney's folks are raising so much more," the supporter said. "I just don't think there's a lot of high-dollar money left on the table."
Federal Election Commission records show Obama has spent $70.8 million in June alone, and with less than a month to go before national party conventions begin, presumptive Republican presidential nominee Mitt Romney and the GOP has about $25 million more in cash on hand than the Democrats.
Obama's team opened a field office in Chillicothe, Ohio, about eight months earlier than it did in 2008, the Times reported.
"The earlier the better," said Adam Fetcher, an Obama campaign spokesman. "Starting a conversation with a persuadable voter months before election day allows us to be more effective in responding to that voter's priorities than if they first hear from us a few weeks out. Building and maintaining our grass-roots foundation takes time and resources, but we believe those early investments will make a difference."