In recent years, the political memoir has become a steady source of income for publishers and insider gossip for readers. Whether you think politicians are simply “cashing-in” on their time in power, or passing on their wisdom, here’s how the political memoir became a weapon and why. What used to be the luxury of former prime ministers has since become a legitimate tool for revenge and reinvention. On the day of her resignation as British Prime Minister, Margaret Thatcher committed to writing her memoir. Three years and £3.5 million later, The Downing Street Years hit the shelves…