There is a logic in simply letting Vladimir Putin have his own way in Ukraine, and thinking no more about it.  After all, Ukraine is not a stable entity.  It is divided on east-west lines – linguistically, religiously, politically and culturally.  Economically, it is dependent on Russia with which, as Lord Risby has pointed out on this site, it conducts half its trade.  Its political elites, like Russia’s, are corrupt (which Kiev’s friends in the west tend to skirt round).  Crimea, so recently seized by Putin, was itself part of Russia until the 1950s.

The Russian leader himself is no Soviet totalitarian, which is why viewing the Ukrainian conflict through the lens of the cold war is mistaken.  Rather, he is an old-fashioned authoritarian autocrat, who is determined not to let Ukraine slide from Russia’s sphere of influence – an aim which, because of the nature of its economy, he is in a position to achieve.

Aiming to get Ukraine into NATO might well mean war with Russia.  Does anyone seriously believe that British voters would support such a conflict, or that they should?  Arming Kiev, instead of this measure or in the meantime, would mean stoking a war that only Putin could win.  In any event, the present crisis was sparked not by Putin, but by the EU: in offering Ukraine a trade agreement without financial backing, it set in motion the events that have now seen Angela Merkel and Francois Hollande fly to Moscow and fly back empty-handed.

It follows from this logic that sanctions should be lifted, Ukraine be left to its fate, and Putin be cosied up to, since we need Russia’s help in containing Iran’s nuclear ambitions, in keeping the lid on Afghanistan, and in the broader struggle against Islamist extremism.

All this is a timely illustration of the degree to which logic depends on the premise it is built on.  Yes, it would be wrong to extend NATO into Ukraine, thereby making commitments that the British people, not unreasonably, are unwilling to underwrite.  And, yes, it would be irresponsible and dangerous to stoke a major war in Ukraine, since only Putin could win it – at least, without the NATO intervention for which there is no democratic mandate.

However, the presumption that Putin is a rational actor, and that he will be satisfied by keeping his grip on Ukraine, is questionable.  He will know well that, while America and the French/German axis have differences over Ukraine, their peoples alike are wary of foreign wars after the Iraq and Afghanistan experiences.  Furthermore, western Europe has demilitarised.  Britain, with France, is one of only two military powers worthy of the name.  Our recent record in the field has been patchy, and growth in our defence budget has been scaled back – which is why senior MPs are calling for a “one per cent per annum increase in the defence equipment budget”.

The danger is that Putin moves on from Ukraine, and seeks to destablise other countries, such as the Baltic States – which are in NATO, and which we are therefore committed to defend.  They need arms and assistance. There is evidence that these are being provided.  And while Russia has legitimate interests in Ukraine, seizing territory and ratcheting up conflict is an illegitimate response.  David Cameron is right to argue that sanctions should be intensified.  As his absence in Moscow showed, there is little else that he is in a position to do.