Experts say the Ukraine call could be the tip of the iceberg – how many more compromising conversations have there been?

What did the president say and when did he say it?

Donald Trump’s politically catastrophic phone call with the leader of Ukraine, sufficient to prompt an impeachment inquiry, might just be the tip of an iceberg that could doom his presidency.

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On Monday it emerged that Trump urged Australia’s prime minister during a recent phone call to help the US attorney general gather information that he hopes will undermine Robert Mueller’s investigation into alleged collusion with Russia.

The White House restricted access to the call’s transcript to a small group of presidential aides, the New York Times reported, noting this was an unusual decision similar to the handling of the July call in which he pressed Ukrainian president Volodymyr Zelenskiy to dig for dirt on a political rival.

It raised questions: how many more compromising conversations have there been? Will the transcripts inevitably leak out with the help of more whistleblowers? And could their combined effect be enough to persuade Senate Republicans it is time to dump Trump, just as an incriminating tape led to the downfall of President Richard Nixon?

“I think the conversations between Trump and world leaders stored in the White House server are critical, and could very well seal his fate,” said Chris Whipple, author The Gatekeepers: How the White House Chiefs of Staff Define Every Presidency.

“A single conversation, recorded in black and white by a notetaker, has already been a game-changer. Trump’s mafia-style shakedown of the president of Ukraine has moved the needle dramatically. If there are other, similarly damning conversations to be found in the White House server, impeachment could gain critical mass in a hurry. And even this Senate might convict when confronted with that kind of evidence: Facts are stubborn things.”

Whipple added: “The House must move quickly to preserve the notes of those conversations.”

Unlike Nixon, or indeed any other US president in history, Trump had no prior political or military experience. His shallow knowledge, short attention span and tendency to wing it have been brutally exposed on the world stage. The public comments at a joint press conference with Vladimir Putin in Helsinki, siding with the Russian president against his own intelligence agencies, were bad enough.

Facebook Twitter Pinterest Trump shakes hands with Putin after their conversation at the summit in Helsinki in 2018. Photograph: Jussi Nukari/Rex/Shutterstock

But what he has said on the line from the Oval Office, White House residence or Air Force One, with officials typically producing a rough transcript straight away, may be worse.

According to CNN, the president’s phone calls with Putin and the Saudi crown prince Mohammed bin Salman so alarmed White House officials that aides took “remarkable steps to keep from becoming public”. This included storing reconstructed transcripts of the calls on “a highly classified computer system” normally intended for closely guarded government secrets.

Last week the Washington Post reported that in 2017, Trump told Russian officials in the Oval Office that he was “unconcerned about Moscow’s interference in the 2016 US presidential election because the United States did the same in other countries, an assertion that prompted alarmed White House officials to limit access to the remarks to an unusually small number of people.”

Then there was the Ukraine call with its request for an investigation into former vice president Joe Biden, a potential opponent in next year’s presidential election. White House officials moved the summary of it to a “standalone computer system reserved for codeword-level intelligence information, such as covert action,” according to an intelligence community whistleblower’s complaint.

A note in the complaint’s appendix said: “According to White House officials I spoke with, this was ‘not the first time’ under this administration that a Presidential transcript was placed into this codeword-level system solely for the purpose of protecting politically sensitive – rather than national security sensitive – information.”

Indeed, the transcripts appeared to have been concealed to avoid embarrassment rather than security reasons. Democrats pursuing impeachment would give much to get their hands on this material, not least the content of the president’s dialogues with Putin, to whom his continued deference remains one of the great mysteries of the age.

Adam Schiff, the chair of the House intelligence committee, told NBC’s Meet the Press on Sunday: “If those conversations with Putin or with other world leaders are sequestered in that same electronic file that is meant for covert action, not meant for this, if there’s an effort to hide those and cover those up, yes, we’re determined to find out.”

But whereas the White House was quick to release a rough transcript of the Ukraine conversation, implying a failure to comprehend its gravity, it is unlikely to be so forthcoming next time. Putin has already warned against it and independent observers warn that such disclosures would set a dangerous precedent, given foreign leaders’ expectations of confidentiality.

Yet secrets find a way, and the political momentum could become irresistible. Elaine Kamarck, a senior fellow in the governance studies programme at the Brookings Institution think tank in Washington, told an audience there on Monday: “It is very interesting how this issue may begin with Ukraine but end with Russia or Saudi Arabia or another country because it has now come out that there are hidden communications.

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“It reminds me of the revelation of the White House taping system during Watergate. Again, it was a throwaway: to was something that nobody ever even knew about, nobody knew it was going to happen. Once it was out there everybody said, ‘Oh, my god! This can do it.’”

The West Wing tapes included the “smoking gun” evidence that Nixon told aides to order the CIA to shut down the FBI’s investigation into a break-in at the Democratic National Committee offices at the Watergate complex. It confirmed testimony by John Dean, the former White House counsel, that Nixon tried to cover up the burglary. The president’s once seemingly invincible support among Republicans collapsed and he was forced to resign before he could be impeached.

While Nixon’s offence was purely domestic, Trump directly solicited the intervention of a foreign power, an act that history may judge to be more heinous. While Nixon’s fate was sealed by big and clunky tapes, the key to Trump’s downfall may be locked in a hi-tech computer server.

Kamarck added: “Now, I would assume that at some point in this process a subgroup of Democrats and Republicans with the properly high security clearances are going to have a look at that server and they’re going to have to say, ‘What’s in here? Is it all covert operations and military movements, or is it something else?’

“What makes you suspicious is that server began to be used the day after the famous meeting between Trump and the Russian foreign minister and the Russian ambassador, where they threw out the Americans and let the Russians stay. So there’s just a lot more to happen here.”