A spokesman for Mr. Horowitz declined to comment. Mr. McCabe also declined to comment. He and his allies have steadfastly maintained that he did nothing improper and cooperated fully with the inspector general.
In October 2016, The Wall Street Journal revealed a dispute between F.B.I. and Justice Department officials over how to proceed in an investigation into the financial dealings of the Clinton family’s foundation. The article revealed a closed-door meeting during which senior Justice Department officials were dismissive of the evidence and declined to authorize subpoenas or grand jury activity. Some F.B.I. agents, the article said, believed that Mr. McCabe had put the brakes on the investigation.
Others rejected that notion. The Journal, citing sources including “one person close to Mr. McCabe,” revealed a tense conversation with a senior Justice Department official in which Mr. McCabe insisted that the F.B.I. had the authority to press ahead with the investigation into the Clinton Foundation.
The inspector general has concluded that Mr. McCabe authorized F.B.I. officials to provide information for that article, according to the four people, who spoke on the condition of anonymity because they were not authorized to discuss the report before it is published. The public affairs office had arranged a phone call to discuss the case, the people said. Mr. McCabe, as deputy director, had the authority to engage the news media.
Such calls are common practice across the federal government when officials believe that journalists have only part of the story. Rather than let incomplete or inaccurate coverage circulate, officials often try to fill out the picture or provide a defense. But Justice Department rules prohibit the dissemination of confidential information, and the inspector general’s report is expected to criticize Mr. McCabe for disclosing the existence of a continuing investigation to The Journal.
When an inquiry uncovers evidence that an agent has violated Justice Department regulations, the inspector general typically refers the matter to the F.B.I.’s Office of Professional Responsibility, which handles questions of punishment.
It is unclear whether the inspector general will identify others who spoke about the Clinton investigation. But Mr. McCabe is by far the most prominent subject. Mr. Trump has taunted him on Twitter, writing in December that he “is racing the clock to retire with full benefits. 90 days to go?!!!” Mr. McCabe is eligible to retire March 18.
Mr. Trump has animosity toward Mr. McCabe for several reasons, including his close ties to the former F.B.I. director James B. Comey, whom Mr. Trump fired last year. But the president is particularly bothered by the fact that Mr. McCabe’s wife, Jill, ran as a Democrat in a failed campaign for a State Senate seat in Virginia. Her campaign received hundreds of thousands of dollars in donations from a political committee run by Terry McAuliffe, the Virginia governor at the time and a longtime ally of the Clintons.
Later, after Mrs. McCabe lost the race, Mr. McCabe was promoted to deputy director and oversaw the Clinton investigation. Though Mr. McCabe sought ethics and legal advice about whether to recuse himself, some in the F.B.I. considered his involvement a conflict of interest. Ultimately, amid scrutiny from the news media, Mr. Comey pressured Mr. McCabe to recuse himself. The inspector general is examining whether Mr. McCabe should have done so earlier.
Mr. Trump has seized on that issue in repeatedly criticizing Mr. McCabe, a lifelong Republican who did not vote in the 2016 election. In face-to-face meetings with Mr. McCabe, the president questioned how he had voted and needled him about his wife. In one instance, he called Mrs. McCabe “a loser,” according to people familiar with the conversation, which was first reported by NBC News.
Mr. McCabe’s allies at the F.B.I. say that Mr. Trump is also eager to discredit Mr. McCabe because he can corroborate Mr. Comey’s accounts of meetings with Mr. Trump.
Mr. McCabe rose quickly through the F.B.I. ranks and was seen as a new model for the second-in-command when he was promoted in 2016. The F.B.I. had transformed from a law-and-order agency to an integral part of the nation’s intelligence apparatus, and Mr. McCabe, who graduated from Duke and Washington University School of Law in St. Louis, was picked not based on a career of street work but based on his intellect and decision-making.
That won him equal parts praise and disdain inside the F.B.I., with longtime agents accusing him of having ascended too quickly.
Mr. McCabe is on leave while he awaits retirement. He was succeeded by David L. Bowdich, the acting F.B.I. deputy director.