If Putin thought he could get away with it, he’d invade Ukraine in the morning

It is not easy to see how matters could be worsened by a parley at the summit.” It was Winston Churchill, during another Cold War between the west and Russia, who coined the term “summit” for a face-to-face meeting of leaders at the highest level.

He was right about that, just as he was to remark that jaw-jaw is better than war-war, and, though virtual and in different times, it’s to be hoped that the conversation between President Putin and President Biden will at least have left both sides better informed about the intentions of the other, or at least their respective stated intentions. As usual, trust is at a premium at the diplomatic summit.

War-war is in the air, however. The formal annexation of Crimea and the informal partial occupation of eastern Ukraine and the Donbas region leaves little room for doubt about the malevolence of Russian designs on the free and independent sovereign state of Ukraine.

The massing of troops in recent months adds a further element of real military and diplomatic-theatrical menace, and skirmishes apparently designed to provoke Ukrainian forces into firing on Russian or Russian proxy forces, to create a bogus casus belli, also suggests that Russia hasn’t exactly ruled out its first invasion of a whole sovereign state since its ill-fated invasion of Afghanistan four decades ago.

Vladimir Putin would surely like nothing more than to bring Ukraine back into the embrace of the Russian Federation. It would please his patriotic but hard-pressed people, and cement his pretensions to be the heir of the tsars and Joseph Stalin.

If Mr Putin thought he could get away with it then he’d invade Ukraine in the morning. The extent to which he thinks he can get away with such a blatant act of armed aggression depends critically on Vladimir Putin’s perceptions of western resistance.

He will recall when President Obama was faced by the Crimea. The western stance, and later response, was too feeble to deter or, still less, reverse that annexation.

Mr Putin will remember well who the vice-president of the United States was at the time. History suggests that the threat, and indeed reality, of diplomatic and economic sanctions do not have a decisive effect on a Russian leader set on sending in the tanks.

Russia and its friendlier satellites seems capable of managing even under the most punitive of sanctions, including those extending to cronies of the Kremlin and their interests in the west. Besides, rogue states – which is what Mr Putin’s Russia is developing into – have ways of evading sanctions, as the cigar and caviar-loving hermit dictator of Pyongyang can attest.

Of course, unlike North Korea or other pariahs, Russia has economic weaponry of its own, namely the supply of natural gas to much of the European Union. So two can play the sanctions game…

Mr Biden and his western allies speak tough to Mr Putin fresh from their unnecessary and humiliating retreat from Afghanistan.

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That does not suggest much resolve in asserting western interests and sticking loyally with an ally and friend in need. Mr Biden, like Donald Trump and Barack Obama before him, seems allergic to foreign “wars without end”, and there is a strong streak of isolationism that runs through American public opinion and the political classes.

Mr Biden is no appeaser, yet he, the French, the British and the Germans show no inclination to do the one thing that would stop Putin in his tank traps – immediate full Nato membership for Ukraine.

All the lessons of the Cold War indicate that such a show of collective strength would deter rather than invite war. Without it, Mr Putin will smell weakness.