The Western nations have realized that Russia's government is now self-confident again. We cannot treat Eastern Europe policy as a low-priority project anymore, it requires some serious attention and effort to achieve further successes in face of Russia.
There's a lot that can be done about the countries whose status is in question; Georgia, Ukraine, Moldavia. Even Belarus might become a hot spot if sometime its government loses power. The strategy formulation for this area will be very challenging.
One option that I would prefer would be a buffer zone of neutral states (comparable to Finland) between NATO and CIS.
But it's not only about the countries that are neither firmly integrated into NATO nor the Russian influence zone.
We have some 'new' NATO allies in Eastern Europe, and never publicly discussed how to secure them against Russia. The NATO border was sufficiently deterring in the past, but the feeling of insecurity seems to be present - especially in Estonia, Latvia, Lithuania and Poland.
This is understandable despite Poland's and Lithuania's distance to the Russian mainland because Belarus is politically extremely close to Russia.
A forward deployment of alliance forces as done during the Cold War when occupation troops in Germany were turned to forward-deployed alliance troops would be a costly option. This option could be used as deterrent, as a price for Russia to pay if it steps over the Rubicon somewhere. Russians don't like foreign armies close to Moscow at all.
To secure Poland requires relatively few efforts in my opinion:
The Polish army needs to be competent in delaying actions, have a good morale and readiness. The German, French, Dutch, Belgian and Danish armies need to be competent in conventional warfare on Polish soil, have a good readiness, good land-bound long-range logistical capabilities and be prepared for quick deployments by rapid deployment exercises (unheralded, whole division and annual if possible).
That should be enough deterrent to secure Poland.
Estonia, Latvia and Lithuania are more challenging; these countries and their armies are rather small. It's unlikely that they could sustain (on their own) an army strong enough to delay an invasion long enough for reinforcements to save the day.
Forward deployment of allied forces would be a simple answer, but that's not really preferable in my opinion.
I suggest to apply the same concept as for Poland, but with some additional physical obstacles in the defensive plan and with enough military aid to enable these alliance members to sustain an army that's strong enough for a long delay of an invasion (they have really only a short distance to trade before they would lose their capital). The logistical supply for the reinforcements should be pre-deployed and supplied by sea. This is especially challenging in Estonia because the Baltic Sea freezes there during the winter.
To add the Baltic states to NATO did certainly not enhance the old alliance member's national security. Such moves do really deserve much more thorough public discussions.
The present situation is that we have the alliance obligation to protect the Eastern NATO members. That should be done in reality, not just on paper. It's about time.
Two interesting articles
"Nato commanders to draw up plans to defend ex-Soviet bloc members from Russia"
"NATO split over Baltic defense"
I made a more detailed analysis of the Baltic scenario. The seaports are surprisingly capable, but there are very few icebreakers and the only permanently free harbor is Klaipeda - easily rendered useless by ground forces direct fire and not very far north. It could help for a counter-offensive, but not in the initial delay& stopping phase.
The river Daugava in Latvia was difficult to cross in past wars - another argument for an invasion during winter.
The seaports will likely not play a major role, just like naval actions in general would have little utility.
The road connection between Poland and Lithuania needs to be improved.
I'll likely post the analysis sometime in the next few months.