AN ADVISER

Meghan O'Sullivan wasn't fooling herself when she helped President Bush craft a new strategy for Iraq that became known as the "surge." The war was going badly, and the idea of sending more troops and shifting focus to civilian security seemed dicey. But at least it offered a chance for success. "All the other options," she recalled, "were about managing defeat."

Few have been more closely involved in the Iraq project than O'Sullivan. At 33, the Oxford graduate headed to Baghdad to serve in the original occupation authority and helped write the transitional law that led to a new constitution. Shunning security, she slipped out of the Green Zone beneath a head scarf to check conditions and to meet Iraq's emerging leaders before returning to Washington as Bush's deputy national security adviser.

With violence down, "cautious optimism" has returned, she said. "In 2006, a lot of Iraqis did not have a lot of hope. And what I'm hearing now is they're getting that hope back."

She acknowledges enormous challenges and costly lessons: "There are many, many lessons. The experience has been very sobering for all of us involved. . . . I've learned there are no easy choices with Iraq. . . . Every choice has serious downsides. They've all got complex consequences and unintended ramifications."

Among the lessons she has drawn: The United States must devote enough troops and civilian resources to match its ambitions. And, she said, "there's no substitute for security. We figured that out the hard way."

O'Sullivan left the White House last fall to teach at Harvard and now sorts through her thoughts in the cloistered environs of Cambridge, Mass. She has not returned to Iraq since September, but it is never far away. "It's hard for me to imagine in my life that a day will go by that I don't think about it," she said.

-- Peter Baker