WASHINGTON — The Democratic head of the House Intelligence Committee, Representative Adam B. Schiff of California, learned about the outlines of a C.I.A. officer’s concerns that President Trump had abused his power days before the officer filed a whistle-blower complaint, according to a spokesman and current and former American officials.

The early account by the future whistle-blower shows how determined he was to make known his allegations that Mr. Trump asked Ukraine’s government to interfere on his behalf in the 2020 election. It also explains how Mr. Schiff knew to press for the complaint when the Trump administration initially blocked lawmakers from seeing it.

Before going to Congress, the C.I.A. officer had a colleague convey his accusations to the agency’s top lawyer. Concerned about how that avenue for airing his allegations was unfolding, the officer then approached a House Intelligence Committee aide, alerting him to the accusation against Mr. Trump. In both cases, the original accusation was vague.

The House staff member, following the committee’s procedures, suggested the officer find a lawyer to advise him and file a whistle-blower complaint. The aide shared some of what the officer conveyed to Mr. Schiff. The aide did not share the whistle-blower’s identity with Mr. Schiff or anyone else, an official said.

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Like other whistle-blowers have done before and since under Republican and Democratic-controlled committees, the whistle-blower contacted the committee for guidance on how to report possible wrongdoing within the jurisdiction of the intelligence community,” said Patrick Boland, a spokesman for Mr. Schiff.

In his whistle-blower complaint, the officer said Mr. Trump pressured the Ukrainian government to investigate a host of issues that could benefit him politically, including one connected to the son of former Vice President Joseph R. Biden Jr.

reconstituted transcript released by the White House of a call between Mr. Trump and President Volodymyr Zelensky of Ukraine backed up the whistle-blower’s account, which was itself based on information from a half dozen American officials and deemed credible by the inspector general for the intelligence community.

Mr. Trump has focused his ire on Mr. Schiff amid the burgeoning Ukraine scandal, even suggesting he could be arrested for treason. The president, who has also made thinly veiled threats against the whistle-blower and accused him of being partisan, is likely to use the revelation that the C.I.A. officer first approached the committee to try to undermine the complaint and suggest it was part of a Democratic plot against him.

The whistle-blower’s decision to offer what amounted to an early warning to the intelligence committee’s Democrats is also sure to thrust Mr. Schiff even more forcefully into the center of the controversy.

On Wednesday, Mr. Trump said Mr. Schiff should be forced to resign for reading a parody of the Ukraine call at a hearing, an act Mr. Trump has called treasonous and criminal.

“We don’t call him shifty Schiff for nothing,” said Mr. Trump. “He’s a shifty dishonest guy.”

Mr. Schiff’s aides followed procedures involving the C.I.A. officer’s accusations, Mr. Boland said. They referred the C.I.A. officer to the inspector general for the intelligence community, Michael Atkinson, and advised him to seek legal counsel. Read more at NY Times