A bolt-from-the-blue invasion may be unlikely but that isn't the last word on the Russian threat:
Estonia's foreign intelligence agency says the likelihood of a military attack from neighboring Russia remains low, but that any confrontation between Russia and the West could quickly turn into “a threat situation for Estonia, Latvia and Lithuania.
Director General Mikk Marran of the Estonian Foreign Intelligence Service said Wednesday that while Moscow wants to refrain from a conflict with NATO, it may opt for "a preventive military offensive" in the Baltic region if it anticipates an escalation of a conflict "even if this occurs in another region".
The Estonians have a point that Russia may worry that a crisis could pose a threat to St. Petersburg.
That's just one reason I don't want a major NATO peacetime deployment to Estonia, Latvia, or Lithuania:
Basically I think that NATO can't really put enough ground combat power in the Baltic states to stop Russia; and if NATO could it would both be seen as a threat to St. Petersburg, prompting even more Russian power threatening NATO there, and be an opportunity to simply attack through Belarus to link up with Russia's Kaliningrad and cut off the best NATO combat units in a Baltic pocket to be reduced at will.
And I'm glad that the Crimea "little green men" takeover scenario has apparently been discarded. I thought it a poor template for Estonia.
But I do worry about the Kargil scenario for Estonia:
Could Russia seek to use their relatively few quality troops on a narrow front rather than try their "little green men" astro-turf revolt tactic again that we will be more attuned to reacting to if applied to Estonia, a member of NATO, with its relatively large (a quarter of the population) ethnic Russian minority?
What if Russia attempts a page out of Pakistan's long territorial struggle against militarily superior India in the 1999 Kargil War?
What if Russia sends in their regular troops--while denying they are their troops--to seize the Estonian ethnic-Russian city of Narva on the northeast border and dares NATO to counter-attack, which would devastate NATO's reputation if we did nothing?
Not long ago, another writer considered that very option.
Russia has options to threaten Estonia. Consider all of them.