Tuesday’s inaugural address marks another astonishing moment for Jon Favreau, the 27-year-old “boy genius” speechwriter who helped craft Barack Obama’s speech to the nation.

Their partnership began with a chance encounter at the Democratic convention in 2004 when Mr Favreau – then a junior staffer for Senator John Kerry, the party’s presidential nominee – told Mr Obama to scrap a line of his speech that duplicated Mr Kerry’s.