The approach Russia generally takes is to act in ways that give them plausible deniability. Not believable deniability, but plausible deniability. Who was really convinced that the little green men invovled in Crimea in 2014 weren't Russian soldiers? That sort of thing generally makes it politically more difficult to respond because there are always groups of people who fall into one of two categories: blithering idiots, and the willfully blind. Combine those groups of people with the groups that would oppose any sort of reaction even if it was a deliberate and publicly announced act of war and it can be more difficult to react.