Gen. David Petraeus, left, and Defense Secretary Robert Gates look on as President Obama announces that Gen. Petraeus will replace Gen. Stanley McChrystal as the top commander in Afghanistan, Wednesday, June 23, 2010, in the Rose Garden of the White House in Washington. On Thursday, July 8, 2010, Mr. Gates said Marine Corps Gen. James Mattis will replace Gen. Petraeus at the U.S. Central Command. (AP Photo/Evan Vucci)

Photo by: Evan Vucci

Gen. David Petraeus, left, and Defense Secretary Robert Gates look on as President Obama announces that Gen. Petraeus will replace Gen. Stanley McChrystal as the top commander in Afghanistan, Wednesday, June 23, 2010, in the Rose Garden of the White House in Washington. On Thursday, July 8, 2010, Mr. Gates said Marine Corps Gen. James Mattis will replace Gen. Petraeus at the U.S. Central Command. (AP Photo/Evan Vucci)