But, Mr. Brennan added, “It clearly, I think, is another indication that Donald Trump is using the Department of Justice to go after his enemies any way he can.”
The Durham investigation has rattled current and former intelligence officers. Little precedent exists for a criminal prosecutor to review the analytic judgment-making process of intelligence agencies, said Michael Morrell, a former acting C.I.A. director who left the government in 2013.
“This whole thing is so abnormal,” Mr. Morrell said.
Prosecutors are ill equipped to assess how analysts work, he added. “The bar for making a legal judgment is really high. The bar for an analytic decision is much lower,” Mr. Morrell said. “So he is going to get the wrong answer if he tries to figure out if they had enough information to make this judgment.”
But other intelligence officials, according to an American official, are reserving judgment about Mr. Durham, who previously spent years investigating the C.I.A. over its torture program and its destruction of interrogation videotapes without charging anyone with a crime. Two detainees died in the agency’s custody.
Mr. Durham is a longtime federal prosecutor who has repeatedly been asked, under administrations of both parties, to investigate accusations of wrongdoing by law enforcement and intelligence agencies. Mr. Trump appointed him as the United States attorney for Connecticut in 2018.
The Justice Department has declined to talk about Mr. Durham’s work in meaningful detail, but he has been said to be interested in how the intelligence community came up with its analytical judgments — including its assessment that Russia was not merely sowing discord, but specifically sought to help Mr. Trump defeat Hillary Clinton in the 2016 election.
The Justice Department inspector general, who released the results late last year of an inquiry into aspects of the F.B.I.’s Russia investigation, found no documentary or testimonial evidence senior law enforcement and intelligence officials had engaged in a high-level conspiracy to sabotage Mr. Trump, the narrative the president and his supporters continue to embrace.