Kamala Harris accepted the Democratic nomination for president and laid out her election pitch to millions of voters at the party's national convention.    As well as offering more of her backstory, she promised unity and to move from the "divisive battles" of American politics.    On this episode, Niall Paterson asks our US correspondent Mark Stone what we learnt about Kamala Harris and how a re-energised campaign against Donald Trump may now play out.Producer: Soila ApparicioEditor: Paul Stanworth