It is good that NATO would consider a military attack as a military attack, no matter how subtle it is:
"The most important work to prepare a nation for the problem of 'little green men', or organizing of Russian (speaking)population, it happens first. It happens now," Breedlove said in an interview published online by German newspaper Die Welt.
"How do we now train, organize, equip the police forces and the military forces of (allied) nations to be able to deal with this?" he said, according to a transcript of his remarks in English provided by NATO.
"If we see these actions taking place in a NATO nation and we are able to attribute them to an aggressor nation, that is Article 5. Now, it is a military response," he said.
One, no NATO state should be in the position of Ukraine, which confronted a subliminal invasion of "little green men" with security forces undermined by the pro-Russian administration that had just been tossed out of power.
Two, hopefully no nation in NATO lacks proper intelligence and counter-intelligence to battle the Russians who would need to prepare the battle space prior to initiating such and invasion.
NATO could help by having para-military national police, intelligence agents, and special forces ready to deploy to eastern NATO countries under such threat.
Three, don't forget that the traditional method of invading is just sending the tanks across the border and the planes flying overhead. Let's be prepared to meet that threat, too--either to stop the initial advance or to gather for the counter attack to liberate the land lost.
UPDATE: And attacks can fall between "little green men" and full-scale open invasion:
Ukrainian government forces engaged with a separatist armored column near the southeastern town of Novoazovsk, about 10 km (6 miles) from the Russian border, Ukraine's military said on Monday.
Ukrainians say 50 armored vehicles crossed from Russia, supported by artillery fire from Russia, but were halted.