IMF chief Kristalina Georgieva joked during a meeting this autumn that the recent arrival of her American deputy had led to a drop in the average age in the room. 

Dan Katz, who took over in October as first deputy managing director of the Washington-based institution, hit straight back. “Yes I’m young,” the 37-year-old said, according to two people familiar with the exchange. “But hopefully we’ll never talk about age in either direction again.”

His riposte to Georgieva, who is nearly twice his age, was light-hearted. But it points to a hard-hitting approach from Donald Trump’s new man at the IMF, as the White House and Republicans in Congress call for sweeping changes in an organisation they have accused of overstretching its mandate and falling victim to “mission creep”.