A former IT aide to New Hampshire Democratic Sen. Maggie Hassan mounted an “extraordinarily extensive data-theft scheme” against the office, the culprit’s plea agreement states. The plot included the installation of tiny “keylogging” devices that picked up every keystroke. Between July and October 2018, former IT aide Jackson Cosko worked with an unnamed accomplice, a then-current Hassan employee, who repeatedly lent him a key that he used to enter the office at night and who allegedly tried to destroy evidence for him. Cosko accepted responsibility for the events revealed by federal prosecutors in court Friday. A statement of facts that...