They talk the talk, but do our leaders have the stomach to face up to the Russians?

Few of us are offered the chance of reinvention at the pensionable age of 65. But in the next few months, Nato, the alliance we take for granted, has precisely such an opportunity. Post-Cold War "coalitions of the willing" in distant Afghanistan (and soon surely against the barbaric Isis in Iraq and Syria) are fine. But nothing beats going back to the job you know best, on your very doorstep: facing up to the Russians – the very reason Nato was created in 1949. But there's one big problem. Does Nato have the will to do so?

The East-West confrontation over Ukraine is the most dangerous crisis in Europe since the 1968 Soviet invasion of Czechoslovakia. You can argue that we, and the US in particular, are in good part to blame, by grossly misreading Russian history, and its memories of Napoleon and Hitler.

It may seem to us pure paranoia: the observation of George Kennan, the great American diplomat who invented the post-war concept of "containment" of the Soviet Union, that Moscow "can have at its borders only enemies or vassals" is as true today as it was in 1946. The fact remains, however, that the West failed to understand that expanding Nato, Russia's sworn foe for half a century, into former Soviet republics would revive these ancestral obsessions.

We got away with it when Russia was prostrate in the 1990s. But that was bound to change. Cometh the hour, cometh Vladimir Putin. And now, we are where we are. Driven by the very nationalist demons he has summoned up, Putin cannot back down. As in every such confrontation, the need to maintain credibility and not to lose face has become paramount.

Yes, the West can apply non-military pressure. But economic sanctions, however high we ratchet them, are unlikely to bend a country as inured to privation as Russia, especially when its leadership, in virtually total control of the media, insists the suffering is justified by a noble patriotic cause, of protecting "the Russian world".

And the problem is not so much Ukraine, which is not a member of Nato and for which the West will never go to war. The true potential flashpoint is the Baltic trio of Estonia, Latvia and Lithuania, former Soviet republics which do belong to Nato, and which, in the case of the first two, have large ethnic Russian minorities. Under Article 5 of Nato's founding treaty, the alliance is obliged to come to the assistance of a member who has been attacked. Suppose the Russians in Estonia or Latvia rise in protest at some real or manufactured grievance against the government in Tallinn or Riga, and their protector in the Kremlin acts as he has done in eastern Ukraine. Would Nato have the will to stop him?

The decision at the Newport summit to set up a rapid response team, of some 4,000 men and based "in Eastern Europe", is hardly an answer. Supplies and equipment would be stockpiled at the base, allowing a so‑called "spearhead" force to deploy quickly. Whether it would be quick enough to counter an invasion by overwhelming Russian forces, is another matter. Presented with a fait accompli, what would the alliance do?

Nor should we yet take too much comfort from Friday's agreement between Russia, Ukraine and the rebels in the east. Such a deal, unless swiftly built upon, risks merely "freezing in place" the conflict, and permanently destabilising Ukraine. What of a similar frozen-in-place war in the Baltics: how would Nato react? The semantic shilly-shallying over whether Russia's actions in Ukraine qualifies as an "invasion" is not an encouraging sign. As for Nato's announcement that it will hold its next summit in Warsaw in 2016, that is no more than a symbolic sop.

Few are more anxious than Poland, the country that has among the bitterest experience of what it means living next door to Russia. What it wants is a "tripwire", similar to the 28,000 US troops stationed in South Korea, or the million-odd troops Nato had in West Germany at the height of the Cold War.

The Poles aren't asking for anything on that scale, merely a couple of permanently stationed combat brigades, with a total strength of about 8,000 men. But their function would be the same: a guarantee that a Russian attack would automatically trigger a direct confrontation between Nato and Russian troops – something that never happened throughout the Cold War.

It is, of course, absurd that Europe on its own cannot cope with Russia, a country with less than half of Europe's population and a total economy the size of Italy's. For that, thank endless defence cuts, born of the wishful belief that war is no longer an option. But again, we are where we are. Nato needs leadership, and for better or worse, that can only come from the US.

This brings us to the other great question of the moment: is Barack Obama, with his professorial detachment and instinctive caution, the person to provide that leadership? "Speak softly and carry a big stick," was the famous foreign policy dictum of Theodore Roosevelt. No one doubts the size of the US stick; the issue is whether the president who wields it is speaking too softly. Or it was until Wednesday.

Presidential trips and foreign summits produce much blather. And so it has been this time. But not when Obama went to Tallinn last week and promised the Baltic republics that, after losing their independence once before (in 1939), "with Nato, you'll never lose it again".

Article 5, he went on, was "crystal clear". An attack on one was an attack on all. "So if, in such a moment, you ever ask again who'll come to help, you'll know the answer: the Nato alliance, including the armed forces of the United States of America. Right here, present, now." Those words are up there with Britain's commitment to Poland in 1939. But does the man who ignored his self-imposed "red line" over Syria's use of chemical weapons, have the courage of his words?

That is a judgement for the man in the Kremlin. Does Obama have the will? Does that pensioner called Nato? But if the alliance can reinvent itself, the result would be the one Putin fears most: a West that finally has the courage of its proclaimed convictions.