The killing of Alexander Litvinenko was “probably approved” by Vladimir Putin. We suspected that already, of course: Your average hired thug doesn’t exactly have access to radioactive polonium, much less use it to murder an FSB defector in broad daylight in the middle of London.

But the official inquiry into his death has now given a definitive verdict about how it happened, and who was to blame — or as definitive a verdict as can be expected.

Theresa May, in a statement to a mostly empty House of Commons, denounced Russia in the strongest possible terms. But the U.K. home secretary didn’t exactly specify what would be done, beyond giving the ambassador a stern talking to — presumably because Russia’s limited co-operation over Syria is too valuable to be jeopardized.

It was a point seized on by Labour’s Andy Burnham, who accused her of “appeasing” Putin and suggested the expulsion of every FSB agent from Britain and stripping Russia of the right to host the 2018 World Cup.

To which the near-universal response was: Has Burnham shared that view with his leader? Even as his MPs condemned the “murderous kleptomaniac regime in Russia,” Jeremy Corbyn remained silent.

The hard Left’s admiration for Russia survived the end of the Cold War undented. And it isn’t just Putin.

This is entirely understandable. The fact that the Russian state, or elements within it, assassinated a British citizen (as Litvinenko had become) on British soil is distinctly awkward if you are a political leader who has made regular appearances on the state-owned Russia Today network. Especially if your chief adviser, Seumas Milne, has not only written endless pro-Putin columns but shaken his hand and shared his stage.

As Rachel Sylvester pointed out in an excellent column in the Times this week, the hard Left’s admiration for Russia survived the end of the Cold War undented. And it isn’t just Putin. The basic setting of Corbyn’s view of foreign policy is to blame everything on the West (especially Britain and the U.S.) and see the rest of the world as its victims. Russia, Venezuela, Bolivia, Iran — in Corbyn’s world, they’re Asterix, and we’re the Romans.

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I hadn’t quite realized how pathological this worldview was until I came across a resolution approved by the Stop the War Coalition, the umbrella group of left-wing extremists set up to oppose the U.S. invasion of Afghanistan and every military intervention since. Adopted at its AGM in September, it blamed the Korean peninsula’s problems on “the interference, aggression of the U.S. and its allies” — referring to a “criminal U.S. embargo against the DPRK… innumerable acts of espionage and aggression… the military presence of… close to 30,000 troops.”

Yes, you read that right. The Stop the War Coalition — chaired, until days before the resolution was adopted, by Jeremy Corbyn himself — believes that North Korea, the most nakedly criminal regime on the planet, is just another victim of American imperialism.

This attitude helps explain the background to the latest flashpoint in Labour’s rolling civil war — the renewal of Britain’s Trident nuclear deterrent.

Corbyn’s recent reshuffle may have been a presentational shambles, but he did win one clear victory: to secure the replacement of Maria Eagle with Emily Thornberry as shadow defense secretary — in Labour jargon, replacing a “multilateralist” (who wants to wait for everyone else to junk their nukes) with a “unilateralist” (who wants to ditch them straightaway).

The problem is that while Corbyn might oppose Trident, it is currently Labour policy to support it. It is also the public’s position.

And it is the position of Corbyn’s union backers, whose members will be welding the hulls of the submarines together. So powerful is their voice that Corbyn was forced to make the bizarre compromise that the subs could be built (to protect the union jobs) but only without missiles on board.

Aside from this strange proposal, Corbyn’s position on disarmament is intellectually coherent. If you believe that Vladimir Putin is a good guy, or at least a misunderstood victim of Western aggression; that Kim Jong-un is being provoked by the White House; that the mullahs in Tehran are actually pretty nice chaps, you certainly don’t need a nuclear deterrent — because you’re rather fond of all the people it’s meant to deter.

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As it happens, there is a case against Trident that the public might accept: that with cash so tight and the rest of the military having suffered such heavy cuts, it makes more sense to beef up our conventional forces than build expensive submarines that will probably never be used.

It’s an argument that’s been made by, among others, Lord Guthrie, former chief of the defense staff. But it’s a hard one to make when you believe, as Corbyn does, that those conventional forces should never be used, either — save for handing out humanitarian aid.

It may seem strange to single out foreign policy as Corbyn’s weak point when, electorally speaking, he is all weak point: The latest polls are historically dire for Labour. But actually, some of his domestic agenda is quite popular: promises to support the NHS, tax the rich, nationalize the railways, build more houses and reduce inequality always go down well.

There has, in other words, been a power struggle within the Corbyn team between the pragmatists and the zealots. And the zealots, led by Milne, have won.

Foreign policy is Corbyn’s real Achilles' heel. Not just because what he thinks runs so counter to the settled views of the British people, but because he insists on saying it.

The most obvious example came in the wake of the Paris attacks, which Corbyn responded to with a riot of vacillation. Then, mid-January, he was asked about the Falkland Islands. He could have deflected the question. Instead he said that yes, he wanted talks with Argentina, and no, the Falkland Islanders wouldn’t have a veto (the exact opposite, as it happens, of his long-held position on Diego Garcia islands).

And if anything, we are going to be hearing more of this kind of thing, rather than less. Neale Coleman, Corbyn’s head of rebuttal, has now quit. There are reports that Simon Fletcher, his chief of staff, may follow. Both worked for Ken Livingstone when he was mayor of London, where they proved skillful at marrying socialist principles with pragmatic politics: allying with Hugo Chávez, but also getting the buses to run on time.

There has, in other words, been a power struggle within the Corbyn team between the pragmatists and the zealots — between accommodation with the voters, and letting Jeremy be Jeremy. And the zealots, led by Milne, have won.

All of which leaves the Labour Party in the hands of this country’s most prominent apologist for a man Britain’s government believes carried out cold-blooded murder on its soil — and further away from electability, and credibility, than ever.

Robert Colvile is a regular contributor at POLITICO.