As the Justice Department investigated who was behind leaks of classified information early in the Trump administration, it took a highly unusual step: Prosecutors subpoenaed Apple for data from the accounts of at least two Democrats on the House Intelligence Committee, aides and family members. One was a minor. All told, the records of at least a dozen people tied to the committee were seized in 2017 and early 2018, including those of Representative Adam B. Schiff of California, then the panel’s top Democrat and now its chairman, according to committee officials and two other people briefed on the inquiry. Representative Eric Swalwell of California said in an interview Thursday night that he had also been notified that his data had been subpoenaed... The zeal in the Trump administration’s efforts to hunt leakers led to the extraordinary step of subpoenaing communications metadata from members of Congress — a nearly unheard-of move outside of corruption investigations. While Justice Department leak investigations are routine, current and former congressional officials familiar with the inquiry said they could not recall an instance in which the records of lawmakers had been seized as part of one. Moreover, just as it did in investigating news organizations, the Justice Department secured a gag order on Apple that expired this year, according to a person familiar with the inquiry, so lawmakers did not know they were being investigated until Apple informed them last month.