Last week, Graham Platner, a progressive Democrat running for the US Senate in Maine, responded to a burst of online criticism by doing something few candidates for high office are ever required to do: he posted a topless photo of himself on the internet. It was an unusual moment in a campaign that had so far gone his way. Platner had won praise from progressives and secured the backing of Bernie Sanders. But his campaign came unstuck when a video surfaced of him dancing in his underwear at his brother’s wedding – and revealing a skull-and-crossbones tattoo on his chest....