Work expands to fill time

US antitrust regulators have time on their hands. The boom in mergers and acquisitions has subsided, so there will be fewer new cases for the bureaucrats to scrutinise even though, after an eight-year hiatus, they have the backing of a more interventionist administration. So what to do? Perhaps they will revisit the past. Christine Varney, Obama’s pick to run the antitrust unit at the Department of Justice, said she was “absolutely” open to retrospectively studying the effects of approved merger...