Putin will be well aware of Donald Trump's periodic disdain for Nato and he may have calculated that a low-key attack on say, Lithuania, is not going to trigger Nato's mutual self-defence clause – Article 5 – and that the US will not respond.

In which case it would make sense for part of the CIA chief's unexplained mission to Moscow was to remind Russia that the US is still fully committed to Article 5.

Lithuania is of special interest to the Kremlin as it has a common border with Poland known as the "Suwalki Gap". Just 60 miles long, this strip of land is all that separates Russia's client state Belarus from its nuclear-armed exclave of Kaliningrad, which is separated from mainland Russia.

If Russia were to seize that it would effectively cut off those three Baltic states by land from their Nato neighbours.

Then there is the question of tactical nuclear warheads. It has long been said that Russian military doctrine views these small but highly destructive weapons as an integral part of its order of battle.

Moscow has been warned off, by friend and foe alike, not to break the 81-year long taboo on using nuclear weapons in anger.

Yet this could still be a tempting option for Vladimir Putin to "escalate to de-escalate" by demonstrating to Ukraine that it has such catastrophic weapons at its disposal it would be better for Kyiv to capitulate to Moscow's terms now or face annihilation.

Of course, in the absence of any clear, attributable, official confirmation from the US as to what this sudden CIA dash to Moscow was all about then it is always possible it was about something else.

That could be trying to persuade Russia to end its military cooperation with Iran, for example, or maybe about more prisoner swaps or the prospect of a mass mobilisation of Russian troops.

But make no mistake, this trip was highly unusual and it came at a time of rising tension between Moscow and the West. Something is almost certainly up.