Former Director of National Intelligence James Clapper James Robert ClapperOn China, Biden is no Nixon — and no Trump The Hill's 12:30 Report - Speculation over Biden's running mate announcement Trump slams former intelligence officials to explain 'reluctance to embrace' agencies MORE said Sunday that he thinks former CIA Director John Brennan John Owen BrennanJournalism or partisanship? The media's mistakes of 2016 continue in 2020 Comey on Clinton tweet: 'I regret only being involved in the 2016 election' Ex-CIA Director Brennan questioned for 8 hours in Durham review of Russia probe MORE's rhetoric is becoming an issue "in and of itself."

"John and his rhetoric have become an issue in and of itself," Clapper said on CNN's "State of the Union." "John is subtle like a freight train and he’s gonna say what’s on his mind."

Clapper's comments came in response to an op-ed penned by Brennan in The New York Times this week, in which he wrote that President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE colluded with Russia during the 2016 election.

Clapper said he empathized with Brennan, but voiced concerns for Brennan's fiery rhetoric toward Trump and his administration.

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"I think that the common denominator among all of us [in the intelligence community] that have been speaking up … is genuine concern about the jeopardy and threats to our institutions," Clapper said.

Brennan's claims drew criticism from some in the intelligence community who said the timing was suspect.

Senate Intelligence Committee Chairman Richard Burr (R-N.C.) on Thursday took aim at Brennan for "purport[ing] to know, as fact, that the Trump campaign colluded with a foreign power."

“If his statement is based on intelligence he has seen since leaving office, it constitutes an intelligence breach. If he has some other personal knowledge of or evidence of collusion, it should be disclosed to the special counsel, not The New York Times,” Burr said.

Burr added that Trump has the “full authority” to rescind security clearance if the statements were “purely political and based on conjecture.”

Trump revoked Brennan's security clearance last week, saying that his "lying and recent conduct characterized by increasingly frenzied commentary is wholly inconsistent with access to the nation’s most closely held secrets and facilities, the very aim of our adversaries, which is to sow division and chaos."

The widely criticized move was seen as a punitive measure against one of Trump's most outspoken critics.

More than 60 former intelligence officials on Friday denounced Trump's decision, stating that ex-intelligence officials should have the right to express their opinions on national security matters without punishment.

"All of us believe it is critical to protect classified information from unauthorized disclosure," the group wrote in a letter obtained by CNN. "But we believe equally strongly that former government officials have the right to express their unclassified views on what they see as critical national security issues without fear of being punished for doing so."

Clapper this week also criticized the Trump administration for its decision, joining more than a dozen high-ranking intelligence officials who signed a letter censuring the president for the move.

—Updated 12:03 p.m.