Alexander Vindman remembers the phone call – and what he did next. Serving on the national security council (NSC), he went to see his twin brother, who was the council’s senior ethics official, closed the door and told him: “Eugene, if what I’m about to tell you ever becomes public, Donald Trump will be impeached.”

Vindman had set up a call between Trump and Ukraine’s new president, Volodymyr Zelenskyy, in July 2019. He heard the US president attempt to leverage US military aid to the country in return for Zelenskyy launching an investigation into Joe Biden’s son, Hunter, over his position at a Ukrainian gas company.

Trump was indeed impeached for offering a quid pro quo in the hope of finding dirt on a political rival. But six years on, the incident haunts current negotiations over ending Ukraine’s war with Russia, including a deal for continued US military aid in exchange for access to Ukraine’s valuable mineral resources.

With Zelenskyy due to visit the White House on Friday, observers warn that Trump is trying to strong-arm him again.

“In the course of this one phone call, President Trump implicated himself by saying that Ukraine would have to do him a favour in order to get access to the congressionally appropriated $400m and a meeting,” recalled Vindman, author of a new book, The Folly of Realism: How the West Deceived Itself About Russia and Betrayed Ukraine. “How much that rhymes with what’s going on this Friday with President Zelenskyy coming in – and another kind of shakedown for billions of dollars in order to continue to receive support.”

Vindman was the NSC’s director of European affairs at the time of the phone call which Trump later described as “perfect”. After informing his brother, he filed a formal report about Trump’s “corrupt scheme” that led to televised hearings and Trump becoming only the third president in history to be impeached by the House of Representatives, though he was subsequently acquitted by the Senate.

The news was monumental at the time but has been somewhat eclipsed in collective memory by Trump’s second impeachment, Russia’s invasion of Ukraine in 2022 and Trump’s return to the White House last month. Trump’s allies and the rightwing media have also worked relentlessly to denigrate both the impeachment and the Russia investigation – in which Ukraine also played a leading role – as hoaxes.

The Trump-Zelenskyy relationship, so cordial in 2019, has soured fast. When America’s top diplomat met his Russian counterpart in Saudi Arabia last week to discuss an end to the Ukraine war, Ukraine was not in the room. When Trump claimed that Ukraine was to blame for Russia’s invasion, remarks that echoed Kremlin talking points, Zelenskyy said Trump was “trapped” in a Russian “disinformation bubble”.

Trump responded furiously, branding Zelenskyy a “dictator” for not holding elections during wartime, when swaths of Ukraine are under Russian occupation, its soldiers are on the frontlines and the country is under martial law.

Earlier this week, in a stunning shift in transatlantic relations, the US split with its European allies by refusing to blame Russia for its invasion of Ukraine in votes on three UN resolutions seeking an end to the three-year war.

Under this shadow, Zelenskyy is due to visit Washington on Friday to sign a deal that, in Trump’s framing, would give the US access to Ukraine’s deposits of so-called rare earth minerals – used in the aerospace, defence and nuclear industries – as a way of Kyiv paying back for aid already sent for the war effort under Biden.

There are similarities with the first quid pro quo – but also differences. Vindman reflected: “He’s not shaking down Ukraine to steal an election this time. There is a national security element. The US needs rare earths for the economy. Ukraine needs investment. So this one actually, in some strange way, even though the scale is magnified, is far more legitimate than the last go around – even though it does come across as a shakedown and completely anti-American in the way we do business around the world.”

Zelenskyy also finds himself in a changed, more vulnerable position. He has said more than 46,000 Ukrainian soldiers have been killed and more than 390,000 wounded, but other estimates are far higher. Trump’s intemperate rhetoric has hurt morale. Russia is making advances on the battlefield.

Max Bergmann, director of the Europe, Russia and Eurasia Program at the Center for Strategic and International Studies thintank in Washington, said: “Ukraine is far, far more desperate than it was in 2019. We have a country that is being assaulted and pummeled by the Russians every minute, so the stakes could not be higher for Ukraine.”

The minerals deal was a perfect example of how difficult it is for Ukraine to navigate the situation, added Bergmann, a former state department official. “The Ukrainians realised that not signing this deal, which is very hypothetical and wouldn’t really come to fruition – companies aren’t going to begin excavating until there’s an actual peace settlement – wasn’t worth fighting over. But it also further demonstrates the lack of interest and commitment that the US has to supporting Ukraine.”

Trump’s first month on the foreign policy stage has come at a head-spinning pace, with plans to take over and redevelop Gaza, buy Greenland from Denmark, seize the Panama canal and absorb Canada as the 51st state. But nothing is more contrary to the Republican party of old than Trump’s willingness to side with Russia over democratic allies.

Joel Rubin, a former deputy assistant secretary of state, said: “We don’t know yet about any personal benefit per se to the president but we do know that he’s using the threat of withholding of military aid and American support for Ukraine in this process as a pressure tactic to extract concessions. That’s typically what you do with your adversary. In this case also it’s not at all clear who would get the money. How does this work? How does this advance America’s global standing and our economy?”

At a cabinet meeting on Wednesday Trump hailed the minerals deal as “a very big agreement” and on Thursday, at a meeting with British prime minister Keir Starmer, he suggested that the presence of American workers extracting critical minerals would act as the kind of security backstop that allies are seeking to deter Russia from invading again.

But Rubin is sceptical that an economic agreement will necessarily guarantee Ukraine’s future security. “Who’s to say that Russia wouldn’t decide they’re going to invade Ukraine but before that they’re going to call the United States and say, we’re going to invade and take over Ukraine but that minerals deal you have with Ukraine, we will maintain and we will do it with you? Then they go and invade and the US says, well, as long as we have our deal, we’re OK with it. There’s nothing to prevent that.”