Musadeq Sadeq/AP Photo

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

Chris O'Meara/AP Photo

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

ISAF/Getty Images

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

T. Ortega Gaines/The Charlotte Observer/AP Photo

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

Win McNamee/Getty Images

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

Paul Richards/Reuters

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.

AP Photo/Mary Altaffer

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

Saul Loeb/AFP/Getty Images

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

Dennis C. Enser/Buffalo News/AP Photo

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