McCain sources say Palin has gone off message several times, and they privately wonder if the incidents were deliberate. They cited that she labeled robocalls -- recorded messages often used to attack a candidate's opponent -- "irritating" even as the campaign defended their use. Also, they pointed to her telling reporters she disagreed with the campaign's decision to pull out of Michigan.

A second McCain source tells CNN she appears to be looking out for herself more than the McCain campaign.

"She is a diva. She takes no advice from anyone," said this McCain adviser. "She does not have any relationships of trust with any of us, her family or anyone else."