In American slang, the letter from Atkins & Thomson law firm in London came out of left field — meaning unexpected, odd and strange.

It was a warning not to publish articles containing allegations made by fugitive member of parliament Oleksandr Onyshchenko, who fled Ukraine ahead of being stripped of immunity in July from prosecution for allegedly stealing $64 million from a state gas producer.

Why strange?

Let me count the ways.

Firstly, the letter came on Dec. 10, after we had already published two articles — on Dec. 6 and on Dec. 9 — about Onyshchenko’s explosive corruption accusations against President Petro Poroshenko and his allies.

Secondly, the letter starts out with “To Whom It May Concern,” although it was sent to my work email address. It came from Graham Atkins, a partner in the London firm whose biography says he specializes in “principally suing newspapers and broadcasters for libel or breaches of privacy, or seeking to prevent them publishing such information for his corporate and individual clients.”

Thirdly, the Presidential Administration hasn’t gotten back to me over the weekend on my question to his spokespeople about whether the law firm actually represents Poroshenko, his parliamentary Bloc of Petro Poroshenko and the government of Ukraine, as the letter claims.

And fourthly, I do not know what law would give the president of a democratic nation — the ultimate public figure who routinely espouses his strong support for free speech — the right to prevent publication of such a story.

But the threat from the letter is clear: “We will sue if required and we will hold responsible any broadcaster and publisher for any republications of these libelous allegations in Europe and worldwide, if necessary and appropriate.”

Let’s assume that the president’s denials of Onyshchenko’s allegations are true — that they are simply fabricated as part of a Russian plot to discredit the president and to politicize legitimate criminal charges against the People’s Will member of parliament who used to be an ally of fugitive ex-President Viktor Yanukovych.

The place to argue the case is in the public domain, with evidence and arguments, not with a threat of lawsuit and censorship. Additionally, I don’t believe it’s possible to libel presidents — they deservedly get the toughest scrutiny because of the vast powers they wield, whether the criticism is fair or not.

In America, at least, the standard for proving defamation in libel for public figures is rightfully so high that almost nobody bothers suing and those who do don’t win. In the Supreme Court’s New York Times vs. Sullivan decision in 1964, the plaintiff would have to show that the news organization acted with actual malice and reckless disregard for the truth.

That does not even remotely apply in this situation. We have no malice for Poroshenko, who Kyiv Post publisher Mohammad Zahoor publicly endorsed for election in 2014. (The Kyiv Post editorial board did not endorse anyone.)

And we don’t know what the truth is in this matter.

But we do know that Onyshchenko, despite the charges against him, is entitled to the presumption of innocence. He has not been convicted in court. He managed to escape or delay justice because of the time-consuming process for removing a member of parliament’s legal immunity from prosecution, which shouldn’t exist in the first place.

Taking to its logical (or illogical) conclusion, Poroshenko and his lawyers are saying that journalists should ignore allegations against the president made by a member of parliament simply because they say the allegations are rubbish or because the Russians might be behind them.

There’s no reason given other than the allegations are false — from their point of view, which we have reported. We have also reported the very legitimate reasons to doubt Onyshchenko’s credibility in making allegations of widespread bribery of members of parliament, looting of state and private companies and abuse of State Fiscal Service to put pressure on taxpayers, among other claims.

I do not know whether the allegations are true, but they are credible in the sense that they are very consistent with what many people have complained about since the Poroshenko administration came to power in 2014.

The other illogical argument, I believe, coming from the president and this law firm is this: If Onyshchenko has absolutely no credibility and his allegations are “completely false” and not supported by any evidence “whatsoever,” then how can he cause “maximum damage” to the reputations of the president or the government of Ukraine?

Truth is found during a public competition for ideas, facts and evidence — not with threats of censorship and lawsuits. I would have thought that Poroshenko, the owner of channel 5 who stood on the right side of Ukraine’s last two democratic revolutions, should know better. His response, instead, barely rises above the civility and enlightenment of autocrats. In fact, the presidential sensitivity and overreaction leads one to wonder whether at least some of Onyshchenko’s allegations are true.

Sue the Kyiv Post and any other news outlet that reports on Onyshchenko’s allegations? I don’t think the president has thought that one through in terms of how much such a blunder will harm his reputation and simply give more attention to Onyshchenko’s claims.

What I suspect is happening is that Poroshenko wants to show results in fighting corruption. He (and his appointed prosecutor general, Yuriy Lutsenko) are selectively choosing targets that are the most politically expendable and not allies and against whom evidence exists to make criminal charges stick.

However, if Ukraine’s corrupt practices are as intertwined as most people think, going after one “bad apple” invites the kind of retribution, mudslinging and accusations that Onyshchenko — as a former insider — is now only too happy to provide now that he’s been cast aside by Ukraine’s elite.

Adding it all up, it’s no wonder that nobody among Ukraine’s powerful is in prison today for murder or the multibillion-dollar theft that has impoverished this nation since statehood. Looks like we are heading into a new year where a lot of the rich and powerful will go to jail — or, as usual and more likely, no one does.