At the White House Correspondents' Dinner a year ago, President Barack Obama teased Hillary Clinton over her six-figure speeches to Wall Street banks. "If this material goes well, I'll use it at Goldman Sachs next year," he said. "Earn me some serious Tubmans."

Less than 100 days after leaving office, Mr Obama has followed through: accepting a $400,000 speaking fee from Cantor Fitzgerald, the mid-sized investment bank.