Robert Dallek

Late 19th-century populists saw bankers and industrialists manipulating markets to enrich themselves at the expense of small farmers and labourers and favoured political candidates promising economic relief through free and unlimited coinage of silver.

The lifelong health problems of John F. Kennedy constitute one of the best-kept secrets of recent U.S. history - no surprise, because if the extent of those problems had been revealed while he was alive, his presidential ambitions would likely have been dashed.

The historical novelist has to consider what has actually happened, while the SF writer is dealing in possibilities, but they are both in the business of imagining a world unlike our own and yet connected to it.