The final chapter of Joe Biden’s five-decade political career has been mired in questions about his clearly ailing health, and who knew what when. Now, a new puzzle has emerged: why was the president of the United States – one of the most medically scrutinised people on earth – not tested for prostate cancer once in over a decade? Was it, as his team insists, a routine omission for a man of his age, or was it something more calculated?