Washington: It was a heart-stopping moment at the intersection of American politics and intelligence – three spy chiefs confronting a Republican President-elect who for months has been mocking them, to tell him that yes, despite all his bluster, Russia had been rooting for him to defeat his Democratic challenger.

The historic sense of a face-off that likely will inform one of the most vital relationships in Donald Trump's presidency was captured in a blunt observation by former Obama-appointed CIA chief Leon Panetta, who told NBC: "I've never seen anything like this in my lifetime, [with a President-elect] undermining the credibility of the very intelligence agencies that have to provide information to him in order for him to be president of the United States."

And to a point, it seemed that Trump might have seen the wisdom of outgoing Vice-President Joe Biden's advice that it was "absolutely mindless" for a new president to feud with the intelligence services – the President-elect was not too vigorous in his comments after the intelligence showdown at Trump Tower in Manhattan.

The guts of the report, by the CIA, FBI and the National Security Agency, was the most detailed formal account to date of what, much to Trump's fury, has been leaked in dribs and drabs in the weeks – that Russian President Vladimir Putin had ordered a huge cyber attack and influence campaign aiming to deny Hillary Clinton the White House.