On the eve of former FBI director James Comey’s testimony to Congress on Donald Trump’s efforts to improperly influence him, Comey’s friend and former US Director of National Intelligence (DNI) James Clapper yesterday used an appearance at the National Press Club in Canberra to savage the President. The president, in Clapper’s view, risked “irrevocable damage” to US institutions. And, in words that immediately echoed round the world, he described the Russian hacking scandal engulfing the president as so large that “Watergate pales” next to it.

Clapper resigned as DNI after Trump’s election (which he admitted came as a major shock to him) and said he was reluctant to criticise a president given he had served both sides of US politics since the Kennedy years, but said Trump was a significant threat to US intelligence services. Clapper said he had “naively” tried to appeal to Trump’s better nature during the handover period following the election by urging him to respect the work of US intelligence agencies, and been disappointed, singling out Trump’s controversial post-inauguration appearance at CIA headquarters as a low point.

How long Trump’s attacks could continue before institutions were “irrevocably damaged” was unclear, he said.

Clapper also declined to warn America’s allies against withholding intelligence in the wake of a series of leaks from the administration, including from Trump himself, saying they had to make decisions that were in their best interests — although he argued the institutional and personal links between Australia and the US remained strong.

However, Clapper delivered his biggest hit on the man he described as a “transitory occupant of the White House” when invited to compare the Russian hacking scandal with Watergate, saying that “Watergate pales compared to what we are confronting now”.

“Wouldn’t it be good if we were friends with the Russians?” Clapper recounted Trump saying to him during his only visit to Trump Tower following the election. Clapper said he agreed that it would be, if the countries’ interests aligned, but that Russia was implacably opposed to the United States.

Clapper famously lied to Congress in 2013 when asked whether Americans’ telephony metadata was being collected by the NSA — his answer “no, not wittingly” prompted widespread claims of perjury and demands for his prosecution when it became clear from the Snowden revelations that the NSA was engaged in mass surveillance of Americans. Clapper later claimed he had given the “least untruthful answer” to the question.

Clapper yesterday also offered some detail on the vexed question of government access to encrypted communications, agreeing that the recent loss of backdoors and hacking tools by both the CIA and the National Security Agency made for a difficult problem to which he had no answer. The NSA was getting better at stopping the “haemorrhage” of leaks, but could never guarantee they would stop. However, he suggested, work had been underway at the end of the Obama administration to develop a proposal for “key escrow” encryption access, in which access to encrypted communications would only be furnished to government agencies by three separate sources combining decryption mechanisms. This would obviate the threat of NSA/CIA-style loss of control of access, although it wouldn’t work on platforms designed from the ground up to prevent proprietors themselves from being able to de-crypt the contents of communications.

He also noted the NSA had established a process for determining whether software vulnerabilities were reported back to software companies or were used to garner “crucial, life-saving information”. However, he said “we’re in a very bad place” on encryption in the United States.