IN THE summer of 1998, as the Monica Lewinsky scandal closed in around him, Bill Clinton was hosting an official White House dinner when he told his guests he needed to visit the bathroom. Excusing himself, he left the table. But, unknown to his guests, he walked in humiliated fury not to the bathroom, but to the White House Map Room. Waiting for him were FBI doctors and a federal prosecutor, there to take his blood sample to see of it matched the DNA on Ms Lewinsky’s now infamous semen-stained dress. This extraordinary episode, which remained secret until yesterday, is...