"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 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.
"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.