Since his campaign headquarters moved to Chicago, Democrats privately said they were concerned that Obama, the party's presumptive candidate, is relying on his inner circle of advisers instead of a broader group that facilitated input from Washington and elsewhere, CBS News reported.

Capitol Hill Democrats told CBS decisions are guarded with secrecy, none more so than the pending vice presidential selection.

"One of the great strengths of this campaign from the very beginning has been the cohesion, the sense of camaraderie, and the lack of drama," said Obama adviser David Axelrod. "And one of the challenges moving forward is to expand and bring in more talent, people from other campaigns and other places, and still maintain that culture we began with."

Some Democrats have griped that Obama is running his own campaign in some states, rather than a coordinated effort and that he hasn't focused on working-class white voters as he pledged during the primaries.

The challenge facing Obama's staff is trying to keep its unity while melding advisers from primary challenger Sen. Hillary Clinton, D-N.Y., and members of other senators' staffs, CBS said.

"There are a whole series of games candidates play," said Dan Pfeiffer, an Obama adviser who recently was named communications director. The Illinois senator, he said, "brooks none of that" and "specifically sought out people who are going to play by those rules."