Hillary Clinton used a moment of brilliantly staged emotion to win the New Hampshire Democratic primary on Tuesday, which every opinion poll had predicted she would lose. As she answered questions in a diner on the morning before the election, Mrs Clinton’s voice began to waver and crack when she said: “It’s not easy ... This is very personal for me.”

Although Mrs Clinton’s supporters dispute that the incipient sobs were shammed, their case is weak. In a decade-and-a-half of national scrutiny, Mrs Clinton has shown no hint of breaking down spontaneously. Emotions can be an electoral trump card, especially if one can show them as Mrs Clinton did, without tears. The key is to appear stirred without appearing weak. Mrs Clinton’s emotion was not only perfectly calibrated but also perfectly timed – for the last newscasts before polls opened in New Hampshire.