In a letter to his top deputy in Iraq, al-Qaida's No. 2 leader said the United States "ran and left their agents" in Vietnam and the jihadists must have a plan ready to fill the void if the Americans suddenly leave Iraq. "Things may develop faster than we imagine," Ayman al-Zawahri wrote in a letter to his top deputy in Iraq, Abu Musab al-Zarqawi. "The aftermath of the collapse of American power in Vietnam — and how they ran and left their agents — is noteworthy. ... We must be ready starting now." Senior U.S. military commanders have said that...