Donald Trump Jr is a curious beast. Of all the hotheads around his hotheaded father, the oldest son leads the charge in confirming the president’s very worst instincts.

If there’s a public spat with the media, you can find Trump Jr throwing his own punches. If there’s an ultra-rightwing gadfly (inside the White House or just on the internet), you can find Trump Jr heartily endorsing their comments.

And now we know: if there’s a Russian stranger offering up dirt on his political opponents, Trump Jr will happily sit down with them.

The younger Donald may have many talents. His Twitter bio cites, for instance, his position as “Boardroom Advisor on The Apprentice”. Those capital letters add a surprising degree of gravitas to this part of his résumé.

But whatever his talents, good judgment is not one of them. Nor is honesty.

First the facts, as we know them so far: Trump Jr agreed to meet with a Kremlin-connected lawyer at Trump campaign headquarters just two weeks after his father clinched the Republican presidential nomination. The meeting took place with the then campaign chairman, Paul Manafort, and Trump Jr’s brother-in-law, Jared Kushner.

When the New York Times first confronted Trump Jr about the meeting, his explanation was that the meeting was primarily about adoptions. He mentioned nothing about a certain presidential candidate called Hillary Clinton.

“It was a short introductory meeting,” he said in a statement. “I asked Jared and Paul to stop by. We primarily discussed a program about the adoption of Russian children that was active and popular with American families years ago and was since ended by the Russian government, but it was not a campaign issue at the time and there was no follow up.”

The next day, when confronted with confidential documents, Trump Jr told a very different story. It is worth reading that new explanation in detail to understand the twists and turns of his mind, at this point in time.

“I was asked to have a meeting by an acquaintance I knew from the 2013 Miss Universe pageant with an individual who I was told might have information helpful to the campaign,” he began in his updated statement. This much is clear: Junior took the meeting with a Russian national because he expected “information helpful to the campaign”.

“I was not told her name prior to the meeting,” he continued. “I asked Jared and Paul to attend, but told them nothing of the substance. We had a meeting in June 2016,” he continued.

This is a curious addition to the narrative. Trump Jr took the meeting without knowing the identity of the person involved, based solely on the word of “an acquaintance” from a Miss Universe pageant. That acquaintance turns out to be a former tabloid journalist called Rob Goldstone, who took a selfie on the day after Trump’s election wearing a T-shirt emblazoned with the giant red word: RUSSIA.

But let’s get back to Junior’s story, shall we? “After pleasantries were exchanged, the woman stated that she had information that individuals connected to Russia were funding the Democratic National Committee and supporting Ms Clinton,” he explained. “Her statements were vague, ambiguous and made no sense. No details or supporting information was provided or even offered. It quickly became clear that she had no meaningful information.”

This is apparently meaningful for the president’s eldest son. It is not in dispute that his intent was to obtain damaging information about the Clinton campaign from a Russian national. His only defense for apparently wanting to collude with an unknown foreign national was that nothing moved forward because she had no supporting information.

At this point, the Russian – a lawyer we now know to be named Natalia Veselnitskaya – changed the subject to the Magnitsky Act and adoptions. Magnitsky represents a series of US sanctions designed to punish Russian officials for human rights abuses, notably the violent death in custody of a lawyer investigating fraud by tax officials. The Russian response was to ban US adoptions of Russian children, among other tit-for-tat measures. “My father knew nothing of the meeting or these events,” Trump Jr concludes.

There is so much that is troubling about this latest version of events that it is hard to know where to begin. By his own admission, the president’s oldest son took a meeting with the most senior campaign officials and Trump advisers with an unknown Russian national. In the months since, the entire Trump White House and campaign denied such meetings vehemently.

Worse, he took the meeting – along with the most senior campaign staff – in the hope and expectation of receiving damaging information about his campaign opponent. All from a Russian national introduced by an acquaintance, with no other background information about her.

This is clear proof both of malicious intent and a desire to collude with Kremlin-connected Russian nationals, whether or not this particular collusion moved forward. Trump Jr was sending a clear signal to Putin’s allies and operatives that he was open for business. He also seems unclear about why Magnitsky involves something that goes far beyond US adoptions of Russian children.

It isn’t hard to see what the alternative could and should have looked like. Ethical conduct has been the standard for presidential campaigns stretching back decades, until the Trumps took center stage.

Consider George HW Bush’s advice to his family in May 1988, at a similar point to Trump’s Russia meeting. “As we move closer to November, you’ll find you’ve got a lot of new friends,” he wrote. “They may become real friends. Or if the polls show Dukakis kicking us – there might be some friendships that will vaporize. They’ll ask for things – ‘Do you know anyone at commerce? Can you call Joe Doakes at state?’

“My plea is this: please do not contact any federal agency or department on anything … I know I must sound very defensive but – believe me – every effort will be made to find some phone call, some inquiry, some letter, that can be made to appear improper.”

There’s nothing wrong with Trump Jr fighting for his father’s election. There’s nothing wrong with him punching back against his critics. You might expect him to do nothing less.

But there’s everything wrong with his ethics, his readiness to lie and obfuscate, and his desire to dig up dirt through any Russian operative who walked through the door.

By doing so, he just moved the whole FBI investigation – and the impeachment machine – several yards closer to the Oval Office. For that alone, his judgment is nothing short of disastrous.