As the U.S. government’s regulatory bureaucracy has ballooned, one agency has been left behind: the office that oversees the regulators. The number of people working in federal agencies with regulatory authority has doubled to about 292,000 under both Republican and Democratic administrations during the past 30 years. In the same period, the Office of Information and Regulatory Affairs, the White House bureau that reviews most major rules, has shrunk to 45 employees from 90, according to data compiled by researchers at George Washington University and Washington University in St. Louis. That means there are fewer people to carry out the...