Newsday says Maria Shriver is the power behind the throne of Arnold, as it describes one chat session about a potential campaign:

According to one who attended, Shriver, a veteran journalist for NBC News, sat at one end of the table, the action star at the other. “She ran the meeting,” this agent said of the grilling, which continued even after Schwarzenegger left the room.
The message: To win Arnold, you had to win over Maria.
Shriver’s strong hand in Schwarzenegger’s professional choices suddenly looms as a factor in California’s political future. As Schwarzenegger deliberates a run for governor on the Oct. 7 recall ballot, nearly a dozen business intimates say the decision will be heavily influenced by a wife who has often functioned as a de facto personal manager.

PS: One reason Arnold might be getting cold feet: “Cameron Blanchard, a spokeswoman for General Electric Co.’s NBC News unit, said executives have had ‘private discussions’ with Shriver about her network duties in the event of a run.” Last year, she campaigned for her brother Mark Shriver for a US House seat in the Maryland suburbs (he was defeated by current Rep. Chris Van Hollen). She only appears on NBC about ten times a year now, mostly on “Dateline.”