“With all the denigration and disparagement and diminishment, I think you are seeing some payback here, not by design but by opportunity,” said Representative Gerald E. Connolly, a Democrat from Washington’s Virginia suburbs who represents many federal employees. “It’s almost karmic justice. All of a sudden, there’s an opportunity for people who know things to speak out, speak up, testify about and against — and they’re doing so.”

Current and former officials like Marie L. Yovanovitch, Fiona Hill and George P. Kent told House investigators how the government was circumvented by a rogue foreign policy operation on Mr. Trump’s behalf. Michael McKinley, a four-time ambassador and senior adviser to Secretary of State Mike Pompeo, described resigning after four decades at the State Department over the treatment of the career foreign service.

Even the original Anonymous is back, the unidentified author of a much-discussed essay in The New York Times last year claiming that officials within Mr. Trump’s administration were working “to frustrate parts of his agenda and his worst inclinations.” The writer, still unnamed, plans to publish a book next month called “A Warning.”