Margaret Mead, the anthropologist, once said: “Never doubt that a small group of thoughtful committed citizens can change the world. Indeed, it’s the only thing that ever has.” It is a truism of modern politics that one person who feels strongly about something has far greater influence on what happens than the 10 people who mildly disagree.

In Microtrends, Mark Penn, one of the US’s foremost political consultants and architect of Hillary Clinton’s presidential bid, takes this axiom to imaginative new levels. Sometimes compared to Karl Rove, George W. Bush’s “boy genius”, whose brilliant microtargeting made all the difference in the 2000 and 2004 presidential elections, Penn comes from a more esoteric background.