The week after the call, the officer delivered a somewhat broad accusation anonymously to the C.I.A.’s general counsel, Courtney Simmons Elwood, according to multiple people familiar with the events. The initial allegations reported only that serious questions existed about a phone call between Mr. Trump and a foreign leader.

As required by government policy, Ms. Elwood had to assess whether a “reasonable basis” for the accusation existed. During the preliminary inquiry, Ms. Elwood and a career C.I.A. lawyer learned that multiple people had raised concerns about Mr. Trump’s call.

Ms. Elwood also called John A. Eisenberg, a deputy White House counsel and her counterpart at the National Security Council, according to three people familiar with the matter. He was already aware of vague concerns about the call…

But as White House, C.I.A. and Justice Department officials were examining the accusations, the C.I.A. officer who had lodged them anonymously grew concerned after learning that Ms. Elwood had contacted the White House, according to two people familiar with the matter. While it is not clear how the officer became aware that Ms. Elwood had shared the information, he concluded that the C.I.A. was not taking his allegations seriously.

That played a factor in his decision to become a whistle-blower, they said.