George Mitchell, Barack Obama’s newly named emissary to the Middle East, on Wednesday faces the biggest challenge of his long career when he begins talks with Israelis and Palestinians amid mounting expectations and deepening uncertainty about his role.

Ready to listen: George Mitchell, left, with Ahmed Aboul Gheit, Egypt’s foreign minister, in Cairo on the first part of his Middle East tour

In five decades in public life, Mr Mitchell has led the Democratic majority in the US Senate, chaired the talks that led to the 1998 Good Friday agreement in Northern Ireland and hunted down steroid use in baseball, America’s national game.