Donald Trump has criticised the outgoing director of the Central Intelligence Agency.
In a series of tweets, the President-elect slammed John Brennan for suggesting he didn't fully understand the threat posed by Russia.
Mr Brennan had earlier appeared on Fox News Sunday to warn Mr Trump of loosening ties with the Kremlin and the dangers of being openly critical of the CIA.
Mr Trump wrote: "Oh really, couldn't do much worse", before listing conflicts in Syria, Crimea, Ukraine as well as "the build-up of Russian nukes".
In a final stinging remark, he also questioned whether Mr Brennan was the "leader of Fake News".
The White House's nominee for CIA chief John Brennan has said he did not try to stop harsh interrogation techniques such as waterboarding when he was at the agency earlier in his career, but had objected to them privately.
Speaking at his confirmation hearing, he said: "I did not take steps to stop the CIA's use of those techniques. I was not in the chain of command of that program".
"I had expressed my personal objections and views to some agency colleagues about ... waterboarding, nudity and others ...
" I did not try to stop it, because it was something that was being done in a different part of the agency under the authority of others, and it was something that was directed by the administration at the time."
The White House's nominee for CIA chief John Brennan has faced Senators at an Intelligence Committee hearing, who will decide on whether he will be appointed to the position.
Protesters interrupted a US Senate hearing where Deputy National Security Adviser John Brennan testified on his nomination to be the director of the CIA.
The protesters were escorted out, after Senator Dianne Feinstein asked for the room to be cleared. The activists were believed to be demonstrating against US drone strikes in Yemen and Pakistan.