Members of US President Barack Obama's national security team have waged an internal battle over Afghan policy that has been marked by bitter infighting, according to a new book by journalist Bob Woodward.
The book, Obama's Wars, also suggests the disagreements were more intense than previously known, The New York Times has reported.
It depicts an administration deeply torn over the war in Afghanistan, with the some of the president's chief advisers doubtful his new strategy will work and quarrelling with each other for much of the past 20 months.
The book describes Mr Obama as a "professorial president" who assigned "homework" to advisers but bristled at what he saw as military commanders' attempts to force him into a decision to triple troop levels in Afghanistan.
Bob Woodward rose to fame reporting on the Watergate scandal, which led to the registration of Republican President Richard Nixon in 1974.
His book reveals that:
The book also discloses that the CIA has a 3,000-man "covert army" in Afghanistan comprised mostly of Afghans who capture and kill Taliban fighters and seek support in tribal areas.