Yesterday in Westminster, Theresa May made perhaps the most transcendental statement of her political career.
In a dramatic scene in the Commons, she effectively accused the Russian state of an act of war by instructing its military intelligence agency, the GRU, to assassinate defector Sergei Skripal in March.
Backed by a large amount of irrefutable evidence about the two Russian intelligence officers who carried out the task, which ultimately resulted in the death of a British citizen and three other serious cases of poisoning, May's claim has enormous implications, not only for the relations of Great Britain with the rudimentary Russian regime, but also for European and Western foreign policy as a whole.
The Salisbury incident is really shocking. It is the first time that a Briton is murdered in our land by a chemical weapon deployed by a foreign power. However, until it happened, Britain seemed completely indifferent to the brutality of Vladimir Putin's government.
Theresa May accused the Russian state of an act of war by instructing its military intelligence agency, the GRU, to assassinate defector Sergei Skripal in March.
After Putin authorized another well-publicized assault on British soil in 2006, when former Russian secret policeman Alexander Litvinenko was killed with a radioactive poison in London, the initial impact and anger soon fell into apathy, thanks to the weakness of the response of our Government. .
It is true that the British authorities rushed to name the Russian suspects, but the speed of this initial announcement did not correspond to a determined action by the Government.
Snorts and snorts at Whitehall produced half-measures, which could only have reassured the Kremlin and the Russian spies that they could escape with the murder.
Since then we have all become aware of the litany of charges against Russia, such as the taking of the Crimea, its bloody intervention in Syria on the side of the tyranny of President Assad and its demolition of the Malaysian MH17 plane over the Ukraine of the rebels in 2014.
But all those atrocities happened abroad, it was argued. They had nothing to do with us, so a slap on the wrists would be enough.
Alexander Petrov (R) and Ruslan Boshirov, who are wanted by the British police in connection with the attack of the nervous agent on the former Russian spy Sergei Skripal and his daughter Yulia
In contrast, since the beginning of the Skripal case, the Prime Minister has been much harsher, imposing sanctions, expelling Russian diplomats, galvanizing NATO and even gaining the support of the White House of Donald Trump and the EU for their actions.
It is true that this was partly because the possible consequence of the Salisbury poisoning was even more serious than Litvinenko's case, since Novichok put hundreds of lives at risk.
However, our Government, despite all its problems with Brexit, has shown a commendable spirit of resolution that has been absent up to now.
Through her clear resolution, Theresa May has launched a direct challenge to Putin's regime.
And although it has taken six months to name the alleged perpetrators, the wait has been worth it.
Thanks to the thoroughness of the investigation, the weight of the incriminating material that could announce in the Commons means that the Russian state can not dissociate itself from its responsibility for this crime.
What his statement also did yesterday was to undo the absurd conspiracy theories about the Salisbury assault that have been circulating, many of them promoted by the Putin regime or by Kremlin sympathizers.
The evidence, gathered by 250 detectives of 11,000 hours of CCTV video, shows incontestably where the fault lies. This raises the question of why the Kremlin resorted to such an act. The answer lies in Putin's security policy, which is so important for his macho political personality and the image of the invincibility of his regime.
As a former intelligence officer of the KGB, he has turned cruelty into a central part of his reputation as a strong man, thus improving his appeal among the Russian people.
When he came to power in 2000, when he was elected president of Russia, there were deep weaknesses in the country's security agencies, personified by the defections of agents like Litvinenko and Skripal.
Since March, he has often wondered why Skripal, a former double agent, should remain a target, many years after Vladimir Putin (in the photo) left him out of the Gulag.
So much information leaked after the fall of communism that Western intelligence thought they had paralyzed Russia's GRU agency, giving MI6 and the CIA a window directly into Russian politics that helped them predict the actions of the Kremlin.
But Putin changed all that through ruthless repression. Internal security was greatly improved and the leaks were closed.
The CIA has admitted in private that many of its contacts in Moscow have remained silent. Some have disappeared. Others simply do not respond to the efforts to contact them.
Dealing mercilessly with defectors is an essential part of that security campaign.
Since March, he has often wondered why Skripal, a former double agent, should remain a target, many years after Putin let him out of the Gulag and allowed him to retire to Britain. It seems that Putin's intelligence services have decided that letting deserters sleep well at night offers too much temptation for others to follow suit.
Killing one, scaring 10,000 is an old tactic, and one that the Russians seem to have adopted. Washington certainly believes that placing the fear of God in potential double agents was the real reason for poisoning Sergei Skripal.
However, the Salisbury attack may also reflect Putin's broader geopolitical strategy, with its focus on dividing the West through surprise, propaganda and intimidation. Years ago, he decided that the West, particularly the United States and Great Britain, wanted to get rid of his regime.
Instead of asking what he could do to dispel Western concerns, he took the opposite course by using the Russian wealth of the country's energy resources, plus the long experience of Soviet spycraft, to mount disinformation and denial campaigns.
Until Salisbury, that strategy seemed to be working.
But the Novichok assault led to an unprecedented act of unity, due in part to the determination of the British Government.
The West remained united and supported Great Britain. The question now is whether this agreement will last. Yesterday, the prime minister said he would try to mobilize the EU to tighten sanctions against Russia and coordinate countermeasures against Russian intelligence operations in Europe.
That could be easier said than done. The wall of the unit is already showing signs of cracking. In addition to the discomfort created by the Brexit, Putin's policy of dividing and conquering is also having an impact, since the Russian president has been making boyfriends with his allies in the EU.
Last month, he was invited to the wedding of the Austrian Foreign Minister, and the right-wing government in Vienna is one of the noisiest voices in the EU clamoring to improve relations with Moscow.
In Italy, the new government is headed by a critic of sanctions against Russia, so imposing new ones is unlikely to win Rome's support.
However, Britain can not allow the Salisbury attack to vanish into oblivion with impunity as it did with the Litvinenko case.
The need for action is even more important because, worryingly, the balance of global power is moving away from the West. The United States, Britain and the EU remain economically powerful, of course, but China's rise as an economic and military superpower adds to the challenge posed by Russia and other states.
Even Turkey, a member of NATO, is moving away from the West under President Erdogan. The fact is that Salisbury's outrage is a graphic indicator that the world is becoming a less stable place. It was a rare but disturbing episode that exposed the nature of the escalation of the global war between espionage agencies.
In its wake, that war is likely to intensify.
Which makes it all the more imperative that the government be robust and vigilant, and that the West remain resolute and united in the face of Putin's cruelty.
MARK ALMOND is the director of the Crisis Research Institute, Oxford.