More than a decade ago, former Senator Russ Feingold described US politics as a system of ‘legalized extortion and legalized bribery’. Running for federal office is so expensive that politicians invariably grow beholden to the millionaires and corporate interests that so kindly fill their campaign coffers.

Feingold’s assessment came before the Supreme Court’s Citizens United ruling in 2010, which enshrined spending limitless sums of money as a form of free speech. That decision struck down a century of precedents that enabled the government to impose restrictions, albeit modest ones, on the wanton buying of elections.