It was as if the sun came out on Wall Street. Donald Trump’s election victory was met not just with a blistering stockmarket rally, but also a flurry of dealmaking. Mondelez, a snack-seller, is reportedly trying to buy Hershey, a chocolatier. Consolidation beckons for the advertising industry. Bankers are expecting that many more tie-ups will follow. The surge in activity partly reflects a level of certainty that would have materialised whoever won the election. But it also has much to do with the changing of the guard at America’s antitrust authorities.