The exodus of senior aides from the White House continued as Gen James Jones, Barack Obama’s head of National Security, resigned. His departure, which comes a week after Rahm Emanuel, the chief of staff, resigned, removes one of the few senior officials not belonging to the US president’s coterie of long-time advisers. Brought in originally for his vast experience and independent voice, it had been clear for some time that the former Nato supreme commander had failed to gel with the president’s inner circle. Gen Jones is being replaced by one of those close aides, his former deputy Thomas Donilon....