TWEETING ON DEFENSE President Barack Obama tweets a question during the Twitter Town Hall in the East Room of the White House, July 6, 2011. Obama said U.S. security and strategic needs must drive impending defense spending cuts. Jack Dorsey, left, Twitter co-founder and executive chairman, moderated the event. SHARE: Download: Full Size (0.07 MB) Credit: VIRIN: 683262-M-BXR50-142.jpg Photo Gallery