Donald Trump is set to face impeachment for a phone call that came to light last month. The crimes he committed in that call were serious, and merit the ultimate sanction that can be imposed on a sitting president, namely removal from office. And yet even since that conversation took place, in fact this very week, Trump has had another call that included an act that may not meet the constitutional standard of “high crimes and misdemeanours” and for which he will face no such punishment – but whose consequences will surely be even graver. For they will be measured in life and death.

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The first of these two fateful calls was, of course, with the president of Ukraine, Volodymyr Zelenskiy, featuring a request that he dig for dirt on Trump’s would-be Democratic opponent, Joe Biden. Even if that demand did not form one half of a clear quid pro quo, in which US military aid and future arms sales to Kyiv would be contingent on compliance – though the grammar of the phone call very much suggests it did – it is still an impeachable offence. The soliciting of foreign interference in US elections has been forbidden since the birth of the republic. It was one of the menaces against which the framers of the constitution were most determined to protect their infant nation.

The second call was Sunday’s conversation with the president of Turkey, Recep Tayyip Erdoğan. This time it was Trump from whom a “favour” was sought. Erdoğan urged Trump to remove a small contingent of US troops from along the Turkish-Syrian border, where they had acted as a kind of tripwire, preventing Turkey from attacking its longtime enemy, the Kurds, in northeastern Syria. Trump agreed, and within hours Turkey was unleashing its full might on the Kurds, the same Kurds who’d believed they were brothers in arms with the Americans in their shared war against Islamic State in Syria. Yes, the losses had been lopsided in that struggle. More than 11,000 Kurds had been killed, while US combat deaths in Syria numbered six. But now their US brothers had abandoned them to their fate.

Current US political chatter is much more about Trump’s pressure on Ukraine than it is about his betrayal of the Kurds, and you can see why. The latest twist in the Ukraine scandal, featuring Trump’s lawyer, Rudy Guiliani, and a couple of characters who ran an outfit called Fraud Guarantee, is compelling: Goodfellas with Russian subtitles. And yet it is the Syria decision that will cost lives, including in ways that may not be instantly obvious.

The most immediate impact will be on those Kurdish forces who, under previous US-Turkish agreements, were only ever lightly armed and who had removed what fortifications they had built along the border. With no air force, no surface-to-air missiles, no armoured personnel carriers, they are massively outnumbered and outgunned by Turkey. Many of them will die. What’s more, Erdoğan has made no secret of his plan to move vast numbers of Arab refugees who had fled from Syria into Turkey over the border. Ankara will call it “resettlement”, and it might look reasonable: repatriating Syrians to Syria. Except these areas are Kurdish. The result, says Carne Ross, the former Foreign Office official whose Independent Diplomat group now advises the Kurds of northeastern Syria, is inevitable: “It’s ethnic cleansing.”

Facebook Twitter Pinterest The deserted Tal Arqam base after the withdrawal of US forces, Ras al-Ein, north Syria, 7 October 2019. Photograph: STRINGER/EPA

Those of us far away can have a more selfish anxiety, too. One of the tasks that had fallen to the Kurds was the imprisoning of former Isis fighters, preventing them returning to combat. Now the Kurds’ limited resources will be too stretched: they can’t both defend themselves from the Turks and act as jailers for a group of Isis fighters, their families and followers that together number 70,000. This is why, says Ross, “Isis prisoners are jubilant – jubilant – at the Turkish invasion,” seeing it as the harbinger of their liberation.

When asked if all these Isis men might now escape and pose a threat elsewhere, Trump’s response was telling. “Well, they’re going to be escaping to Europe. That’s where they want to go.” Meaning if, thanks to me, Isis terrorists are now free to shoot people in Paris or blow up buses in London, that’s not my problem.

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In other words, you can make a good case that the Erdoğan call will have a more lethal impact than the Zelenskiy one, even if it is the latter for which Trump will be held to account. But the two conversations have much in common.

First, they both reveal the readiness of this president to act alone and against all advice, ignoring his military top brass, national security team and Congress. On Ukraine, his own appointees and Republican allies on Capitol Hill were clear that aid to Kyiv was in the US strategic interest. No matter. Trump was ready to withhold $400m in aid if that’s what it took to coerce Zelenskiy into helping his re-election campaign. Similarly, even Trump’s most ardent cheerleaders agreed that the Kurds were allies whose loyalty should be rewarded and that a green light to a Turkish invasion would be unforgivable treachery. No matter, he did it anyway. In both Ukraine and Syria, Trump was ready to jettison long-established US policy to serve his own interests – keeping everyone else in the dark until it was too late.

In Ukraine, his personal motive is clear enough. In Turkey, less so – though it is not irrelevant that there are two “major, major” Trump Towers in Istanbul, giving Trump what he himself once called “a little conflict of interest” when it comes to that country. We have surely seen enough by now to know that when Trump hears a request from an authoritarian leader, especially one who could have business leverage over him, he likes to say yes.

The flipside is his casual disregard for America’s allies. Ukraine is loyal, but was threatened with being starved of cash unless it agreed to act as Trump’s covert opposition research unit. The Kurds have fought valiantly, but Trump brushed them off, saying bizarrely that “they didn’t help us with Normandy”. He approaches all alliances as mere transactions, tweeting that: “The Kurds fought with us, but were paid massive amounts of money and equipment to do so.” As one observer put it, for Trump the Kurds weren’t allies – they were subcontractors. And note the contempt for Europe in both cases. His call with Zelenskiy was full of disdain for the EU; now we know he doesn’t mind Isis terrorists murdering and maiming – so long as they only murder and maim Europeans.

There’s a last connection, too. For who benefits from a Ukraine deprived of cash and military equipment? Why, it’s the same person who benefits from a US pullback from Syria: Trump’s old friend, Vladimir Putin.

Trump’s conduct in these two very different situations – a deliberate political strategy in Ukraine, an apparent whim in Syria – has one common result, namely the further destruction of America’s reputation in the eyes of its allies. It shows that Donald Trump is not just corroding vital democratic norms and conventions in the US. He is also endangering human lives far away from America’s shores. It is not just the US that needs to see him removed from office and soon – it is the whole world.

• Jonathan Freedland is a Guardian columnist