Late last year, Ms. Cutter left her role as deputy senior adviser in the White House to move to Chicago and become one of three deputy campaign managers, overseeing policy, research and communications. In essence, Ms. Cutter has become the chief messenger for the Obama campaign, a loyal soldier who says the things the candidate can’t (or won’t) say — often on YouTube. …

“All Stephanie wants is results,” said an Obama administration aide and friend of Ms. Cutter’s who is not allowed to discuss campaign issues. “She is an old-school, take-no-prisoners political operative. Losing is not tolerated.” (Ms. Cutter has earned the nickname The Ninja at campaign headquarters, since she stealthily inserts herself into battles.) …

In an administration not known for its embrace of outsiders, Ms. Cutter managed to become a trusted aide to both Michelle Obama, whom she worked for in 2008 and in the White House, and Mr. Obama, who pleaded with her to take West Wing and campaign jobs.