For nearly three full days, Bill and Hillary Clinton owned the Democratic National Convention – an extraordinary act of domination by the losers. But late on Wednesday night Barack Obama walked on stage to join Joe Biden, the vice-presidential nominee, and the mood changed with a snap. Mr Obama was tomorrow’s man, the first African-American nominated for America’s highest office by a major party. The Clintons and all their dramas suddenly seemed the stuff of history.

With their own goals in mind, the Clintons played their assigned roles – to heal the divisions they had helped to create. The Obama camp let them stay centre stage for what seemed like an eternity, but it was a Faustian pact. In return, they had to make peace and give him their full support. As they smoothed the way for him, they created a downward political arc for themselves. And, as almost always happens with the Clintons, they gave another intriguing glimpse of their unconventional marriage. In this final act, they were implicit rivals – for the applause of delegates, approval of television viewers and verdict of historians.