CIA director John Ratcliffe travelled urgently to Moscow on Tuesday. The trip was short, not announced in advance, and stripped of the usual protocol packaging - which in diplomacy means one thing: it was not scheduled, it became necessary.

Now an explanation is emerging. Hamish de Bretton-Gordon, former commander of Britain's chemical, biological, radiological and nuclear forces, argues in an analysis for the Telegraph that intelligence points to Vladimir Putin, under pressure from every direction, weighing an attack on one of NATO's European members. And if that fails to frighten Europe into withdrawing its support for Ukraine, the next option on the table, according to the same information, is a tactical nuclear weapon used against Ukraine.

Why analysts are taking this more seriously than before

The nuclear threat from the Kremlin is as old as the war and until now was almost always rhetoric. The difference, de Bretton-Gordon argues, is that after four and a half years Western agencies no longer treat it as pure rhetoric - because the numbers underneath it have changed.

Ukraine has become one of the global leaders in battlefield drone warfare. Its strikes on Russian infrastructure, including oil industry facilities, are complicating exports and fuel supply, and queues are forming at petrol stations in parts of Russia. That is not the picture of a state that is winning.

An even bigger problem than the economy is the army. After heavy losses, Russia is finding it increasingly hard to recruit new volunteers despite high salaries and financial incentives. The analysis assesses that the shortage of people may in time become the single biggest weakness of the Russian war machine.

The mobilisation they keep postponing

The way out is known and the Kremlin knows it: a new, broader mobilisation. Western officials, the analysis claims, believe certain preparations are already under way.

Only, that is where the political trap lies. The burden of mobilisation so far has not been carried by Russia's largest and wealthiest cities - the Russian middle class could watch the war from a relative distance, as something happening to other people. If a new mobilisation reaches a significantly wider part of the population, that distance disappears. And when the war knocks on doors in Moscow and St Petersburg, the political consequences for the Kremlin could be serious.

That is why the author concludes that Putin is no longer waging the war only over a political position, but over his own survival in power and the legacy he wants to leave. That is the key shift - a leader calculating how to win is predictable; a leader calculating how to survive is not.

The Iranian bill and the emptied American stockpiles

Washington enters this equation too, and in a way that does not favour Europe. According to the analysis, Moscow is carefully watching American policy towards Iran and assessing how ready Washington is to be militarily engaged in several crisis areas at once.

More concretely: during the operations against Iran, the United States used up part of its stock of long-range precision weapons. That is a data point the Kremlin does not read as a detail.

Joe Biden's administration previously threatened Russia with "catastrophic" consequences if it used a nuclear weapon in Ukraine. America still has enormous conventional capabilities - but running a large campaign against Iran puts a strain on those same reserves. Two wars competing for the same ammunition.

And Europe?

The analysis concludes that responsibility now falls on NATO's European members, and that Moscow must be told plainly that an attack on an alliance member would trigger a powerful conventional military response. The argument holds up: Russian conventional power has been seriously drained in Ukraine, while the European members together command far greater economic, technological and military potential.

"Together" is the hardest word in that sentence. European defence to this day functions as an agreement in which everyone concurs on the principle and nobody wants to pay first.

For the Balkans this is not distant news from another geography. The region has NATO members, it has states still waiting, and it has long experience of what happens when great powers test where somebody else's resolve ends. The Balkans know this scene by heart - first they check whether anyone will react, then they move in.

Ratcliffe flew to Moscow and flew back. What he took and what he brought we do not know. We only know that the head of American intelligence does not travel urgently when everything is under control.