The investigation, still in its infancy, ground to a halt. After it was revealed that Mr. Nunes obtained his information on White House grounds from White House staff members, Democrats called on him to recuse himself from the inquiry. He eventually did, but only when it emerged that he was under investigation by the House Ethics Committee for possibly leaking classified information. Mr. Conaway, the most senior Republican on the committee, took over.

The encore appearance before the committee by the heads of the F.B.I. and N.S.A. has proved a sticking point. After Mr. Nunes scuttled the public hearing with Ms. Yates and other officials in favor of another round of questions for Mr. Comey and Admiral Rogers, Democrats accused Mr. Nunes of bowing to White House pressure. A series of letters between Ms. Yates’s lawyer and the White House counsel showed that administration officials had tried to block her from testifying before Congress, an accusation the White House spokesman, Sean Spicer, later denied.

Last month, the House committee extended a new invitation to Ms. Yates; James R. Clapper Jr., the former director of national intelligence; and John O. Brennan, the former C.I.A. director.

The panel has not scheduled that public hearing, though Ms. Yates and Mr. Clapper are expected to testify before a Senate panel on Monday.

Days after Mr. Trump took office, Ms. Yates alerted the administration that Michael T. Flynn, then the national security adviser, had misled Vice President Mike Pence and other White House officials about his communications with the Russian ambassador to the United States, and that it could make him vulnerable to blackmail by Russia.

Mr. Flynn, a three-star Army general who was forced out of the administration after less than a month, is now under investigation by the Pentagon’s inspector general over allegations that he failed to disclose payments from a foreign government or get them approved, a potential violation of federal law for a retired military officer.