As Vladimir Putin canters into his fourth term as Russian president, what does he see as he surveys the Atlantic alliance that brought the Soviet Union to its knees? In Germany, Angela Merkel spent almost six months cobbling together a coalition. In France, Emmanuel Macron was obliged to form a new party to keep the threat of the far right at bay. In the US, a buffoon president is under investigation over alleged Russian interference in the 2016 election.

And in Britain? Well, one can only imagine the wintry smile that must flicker across Putin’s features as he is updated on our response to the Salisbury chemical attack. Most absurd of all is the fixation with secondary issues. We fulminate over the brusque language used by the defence secretary, Gavin Williamson (“Russia should go away and shut up”). Even as Sergei Skripal and his daughter Yulia lie critically ill in hospital, Alex Salmond defends the right of Russia Today to broadcast its Kremlin propaganda. There is a furious argument over whether or not Newsnight doctored an image of Jeremy Corbyn’s hat.

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Theresa May’s performance in recent days has been impressive and, perhaps for the first time since last year’s election fiasco, unequivocally prime ministerial. Let us see how she conducts herself this week, as she chairs a meeting of the national security council on Tuesday, representatives of the Organisation for the Prohibition of Chemical Weapons arrive in the UK to test samples of the nerve agent used against the Skripals, and new measures are considered to crack down on criminally acquired Russian wealth laundered in London.

In contrast, Corbyn’s response has been embarrassingly sophomoric. To say as much is to invite seething fury on social media from his disciples. Well, too bad. In December, the Labour leader told Grazia magazine there would “probably be another election in the next 12 months”, which he would “probably win”; and: “I’m ready to be prime minister tomorrow.” Fair enough. So let us judge him on that basis.

In the Commons last Tuesday, his immediate contribution was to issue a pious warning against “letting the tensions and divisions get worse” – as though May had her finger trembling over the nuclear button – and to score cheap party-political points over “donations to the Conservative party from Russian oligarchs and their associates”. In the immediate aftermath of a nerve agent’s deployment on British soil, was party funding really the issue for the self-proclaimed prime minister-in-waiting to put front and centre?

His spokesman, meanwhile, said use of intelligence by governments in the past had been “problematic, to put it mildly”. Then, in a Guardian article, Corbyn returned to the fray to congratulate himself on his opposition to the invasion of Iraq, attack on Libya and war in Afghanistan, and to urge the less enlightened not to yield to “emotion and hasty judgments”. There should be no “drift to conflict”, he declared – though it was unclear who was proposing such a drift.

Being a prime minister is about the determination to get it right and the courage to risk being wrong

At the time of writing, Labour seems simultaneously to be calling for calm and attacking the government for inaction. On Sunday Shami Chakrabarti told the BBC’s Andrew Marr and John McDonnell informed ITV’s Robert Peston that their party agreed, after all, with the prime minister. It was right for the government to expel 23 Russian diplomats, and essential that ministers went further in boxing the ears of McMafia-style oligarchs. At the same time, however, the PM should wait for further “evidence” before stumbling impetuously into a crisis.

I am not quite sure what the clinching “evidence” in such a case would be – other than a Moscow hood called Nikolai turning up at Paddington Green police station with a case marked with skull and bones logo to declare: “OK, guys, it’s a fair cop.” Opposition parties can indulge in the language of deferral and absolute forensic certainty. But when it comes to security, government is all about the balance of probabilities and how you assess them.

Corbyn warns of a “new cold war”. But has he really got over the last one? In his hostility to Nato, the EU and the US, he seems irredeemably attached to the analytic categories of the ideological conflict between east and west that shaped the second half of the 20th century.

The great divisions of the 21st century are very different. Today’s wars are hybridised: a vicious brew of targeted assassinations, cyber-attacks, political disruption and other aktivnye meropriyatiya (“active measures”). In this connection, the Labour leader and his team should read Anton Shekhovtsov’s brilliant new book, Russia and the Western Far Right, to see how sophisticated Putin’s long campaign has been.

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For the Kremlin, the battle is no longer between communism and capitalism, but authoritarianism and liberal democracy. In this great struggle, Russia will exploit whatever assets it finds – whether or not they know they are being used. In some cases, this involves direct or indirect support for disruptive far-right parties. In other instances – such as the Salisbury attack – the objective is to sow political disunity abroad. Mission accomplished.

McDonnell said Corbyn’s Commons performance “wasn’t an attack, it was a critique”. That is a distinction without a difference. The task of a prime minister is not that of an investigative reporter. It is about judging probabilities, responding decisively and in real-time to the imperatives of national security. It is about the determination to get it right and the courage to risk being wrong.

Even the most ethically pure prime minister has to take action in less than optimal circumstances, to make intrinsically unpleasant decisions in which there is no guarantee of success. On this basis, Corbyn looks distinctly ill suited to the job he believes will be his very soon. Putin must be delighted.

• Matthew d’Ancona is a Guardian columnist