For all the aides and armies at his disposal, the commander-in-chief must be - as President George W Bush memorably described it - the Decider. And having made a final decision, a president must then live with the consequences.

Joshua DuBois is the man who has helped President Barack Obama with that process since before he entered the White House. Each day he sends him an email containing an inspirational message with words of wisdom from scripture, history and literature.

Having served as director of President Obama's Faith Based Initiative and informal spiritual adviser during the first term, Mr DuBois has now left to start his own company. He has written a booked called Daily Devotionals and talked to the BBC about how the president still expects a message in his inbox every morning.