21:00Letter from America by Alistair CookeA history of party conventionsBBC Radio 4 Duration: 15 minutes Fri 17th Jul 1992, 21:00 on BBC Radio 4 FMAvailable for over a yearListen nowThree dramatic party conventions from the past, and how the system of choosing a presidential candidate has evolved.GenresFactualArts, Culture & the MediaBrandLetter from America by Alistair Cooke Source: BBC Online