Time served on Wall Street has long smoothed the path to the top job at America’s Treasury. Before he was the first treasury secretary Alexander Hamilton could boast, among other things, a role in establishing the Bank of New York, which is still in business. More recently, and somewhat less heroically, Robert Rubin and Hank Paulson both ran Goldman Sachs, a bank, before taking office. As its name suggests, the “revolving door” sends people in the other direction, too. Mr Rubin went on to hold senior positions at Citigroup, another bank. Cerberus Capital Management and Warburg Pincus, two investment firms, are chaired by John Snow and Timothy Geithner respectively.