US General John Allen, the top commander of US forces in Afghanistan, allegedly exchanged flirtatious e-mails with Jill Kelley.

Jill Kelley, a friend of David Petraeus, allegedly received threatening e-mails from Petraeus girlfriend Paula Broadwell.

Former CIA director Davis Petraeus met Paula Broadwell in 2006, when she was a student at the Harvard Kennedy School of Government.

Broadwell co-wrote the Petraeus biography "All In," and the two began their affair shortly after Petraeus was named CIA director.

Petraeus’ resignation left President Obama, shown with Petraeus in June 2010, searching for a new CIA director.

Secretary of Defense Leon Panetta (right), with Allen (left) and Petraeus (center) in 2011, has indicated he will not stay for Obama’s second term.

Senator John Kerry of Massachusetts, previously considered a contender for secretary of state, may become the next defense secretary.

John Brennan, Obama’s chief counterterrorism adviser, is said to be a strong candidate for Petraeus’ CIA position, officials said.

Michael Morell, associate deputy director of the CIA, could become the director if Brennan declines the job, officials said.