U.S. officials are consumed by what they missed for at least nine months: a hacking. The breach is far broader than first believed, it now appears Russia exploited multiple layers of the supply chain to gain access to as many as 250 networks. The hackers managed their intrusion from servers inside the United States, exploiting legal prohibitions on the National Security Agency from engaging in domestic surveillance and eluding cyberdefenses deployed by the Department of Homeland Security. The government’s emphasis on election defense may have diverted resources and attention from long-brewing problems like protecting the “supply chain” of software.