"It's just appalling and clearly underscores how partisan Mr. Nunes has been," Brennan said in an interview on NBC's "Meet the Press."
"He has abused the chairmanship of [the Intelligence Committee]," Brennan said.
Brennan headed the CIA during a sprawling investigation into Russia's interference in the 2016 election and the Trump campaign's connections to Russia. He said that from his perspective, the FBI was "very forthcoming" with information presented to a court that authorized surveillance on the campaign aide, Carter Page. That surveillance was first authorized in October 2016, a month after Page left the campaign.
Brennan said that he first became aware in the summer of 2016 of a dossier of information about Trump and his Russian connections that had been compiled by a former British intelligence officer. Nunes's memo portrays that dossier as "essential" to obtaining the warrant, but it doesn't specify which portions were used, and Democrats have disputed the accuracy of Nunes's claims.
Brennan said he didn't see the dossier until December 2016, although he knew that journalists were inquiring about it.
"I do think it was up to the FBI to see whether they could verify any of it," Brennan said, but he emphasized that the dossier played "no role whatsoever" in an assessment by all U.S. intelligence agencies that Russia had interfered in the 2016 election. He added that intelligence agencies were also developing their own information on Russia's interference "on multiple fronts" and that the FBI had its own sources of information.
The release of the memo has raised concerns that Trump will use it as grounds for firing Deputy Attorney General Rod J. Rosenstein, who oversees the special counsel probe investigating Trump's ties to Russia and potential obstruction of justice by the president and his aides. Trump sought in June to fire the special counsel, Robert S. Mueller III, but backed off after White House counsel Donald McGahn threatened to resign.
Reince Priebus, the former White House chief of staff, said on "Meet the Press" that he "never felt that the president was going to fire the special counsel," disputing a Washington Post report that he was "incredibly concerned" that Trump was moving to fire Mueller.
"I never heard that," Priebus said. But when pressed on whether he was aware of the president's views on the issue, Priebus said Trump was "clear" about what he saw as Mueller's conflicts of interest in the job and allowed that others may have "interpreted that" as Trump's desire to fire Mueller.