Good question. At the CIA Petraeus could not take his advisers with him, but was surrounded with WH insiders.
http://www.charlotteobserver.com/2012/01/24/2953553/petraeus-bio-takes-a-close-look.html
In June 2010, when President Barack Obama tapped him to take charge in Afghanistan for what would become Petraeus’ final command, Broadwell knew the time was right to parlay her dissertation into a biography.
Soon, she had an agent and a contract from Penguin Press. To help organize and write the book, she teamed with The Washington Post’s Vernon Loeb. Broadwell proved to be an “absolutely intrepid” reporter, Loeb says, dictating from airports, filling up his email inbox and delivering “this fire hose of information.”
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This is her brother, with whom she’s been staying in DC:
http://www.sutherland.com/steve_kranz/
http://www.sutherland.com/newsevents/News_Detail.aspx?News=0941aa31-dbec-477e-8bd3-39836376836b
Buzzfeed also reports that David Petraeuss unofficial press agent, Tom Ricks, helped Paula Broadwell score a literary agent, a publisher and a six-figure deal for her biography.
http://en.wikipedia.org/wiki/Thomas_E._Ricks_%28journalist%29
Thomas E. Ricks