When Barack Obama replaced George W Bush in the White House, US strategy in the Middle East changed - hubris was out, humility was in. But as the region has sunk deeper into violence, extremism and sectarianism, President Obama's limited ambitions have been condemned by critics as a dangerous form of weakness. Stephen Sackur speaks to Philip Gordon, who has just left his role as the White House's coordinator for Middle East policy. What happened to American leadership in a troubled region?