The departing CIA director John Brennan has launched a scathing attack on Donald Trump, warning the President-elect does not fully understand the threat posed to the US by Russia.

"I think Mr. Trump has to understand that absolving Russia of various actions it has taken in the past number of years is a road that he needs to be very, very careful about moving down."

As Reuters reports, Brennan's comments, during an interview on "Fox News Sunday," exposed the simmering tensions between the president-elect and the intelligence community he has criticized and is on the verge of commanding.

"Spontaneity is not something that protects national security interests and so therefore when he speaks or when he reacts, just make sure he understands that the implications and impact on the United States could be profound," Brennan said. "It's more than just about Mr. Trump. It's about the United States of America." "What I do find outrageous is equating intelligence community with Nazi Germany," Brennan said. "I do take great umbrage at that."

Brennan also questioned the message it sends to the world if the president-elect broadcasts he does not have confidence in the United States' own intelligence agencies.

"The world is watching now what Trump says and listening very carefully. If he doesn’t have confidence in the intelligence community, what signal does that send to our partners and allies as well as our adversaries?" "There is no basis for Mr Trump to point fingers at the intelligence community for 'leaking' information that was already available publicly,"

Speaking earlier on Sunday, President Barack Obama's chief of staff Denis McDonough said the intelligence community was "staffed by an unbelievably cadre of professionals" and he dismissed the notion that they would seek to undermine Mr Trump's victory as the President-elect has suggested. As Jacob G. Hornberger warns:

In a truly remarkable bit of honesty and candor regarding the U.S. national-security establishment, new Senate minority leader Charles Schumer has accused President-elect Trump of “being really dumb.”… for taking on the CIA and questioning its conclusions regarding Russia. “Let me tell you, you take on the intelligence community, they have six ways from Sunday at getting back at you…. He’s being really dumb to do this.” […] No president since John F. Kennedy has dared to take on the CIA or the rest of the national security establishment […] They knew that if they opposed the national-security establishment at a fundamental level, they would be subjected to retaliatory measures. Kennedy… After the Bay of Pigs, he vowed to tear the CIA into a thousand pieces and scatter them to the winds. He also fired CIA Director Allen Dulles, who, in a rather unusual twist of fate, would later be appointed to the Warren Commission to investigate Kennedy’s murder. Kennedy’s antipathy toward the CIA gradually extended to what President Eisenhower had termed the military-industrial complex, especially when it proposed Operation Northwoods, which called for fraudulent terrorist attacks to serve as a pretext for invading Cuba, and when it suggested that Kennedy initiate a surprise nuclear attack on the Soviet Union. […] Worst of all, from the standpoint of the national-security establishment, [Kennedy] initiated secret personal negotiations with Soviet Premier Nikita Khrushchev and Cuban leader Fidel Castro, both of whom, by this time, were on the same page as Kennedy. […] Kennedy was fully aware of the danger he faced by taking on such a formidable enemy.

And, as we previously noted, to the extent that President Kennedy consciously stood up to the system, he paid the price for his attempt at independent wielding of power from the Oval Office.

It is a shuddering thought. A sharp lesson in history that must not be misinterpreted.

The implications for Trump are quite clear. If his refusal to take intelligence briefings, or follow CIA advice is serious, then serious consequences will follow. If Trump is serious about peace with Putin when they insist on war, there will be a problem.

The CIA director will likely be replaced by Mr Trump's pick Mike Pompeo next week.