I think there was a precedent for this risk in living memory. I think there was even a term for it... some kind of "war" that wasn't "hot"...

But anyway it would be better if politicians talked about the way in which Russian aggression is already here ("hybrid warfare") because it simultaneously supports how this is not just scaremongering but something that is already happening, and modulates the risk under discussion. It's very unlikely that Russia would open a new front given that it can't make progress on the actual battlefield in Ukraine and is having manpower issues. But could it step up undersea cable sabotage, drone overflights, parcel bombs, terrorist attacks, assassinations, airspace incursions, etc? Absolutely.

And the thing is, those tactics are attractive to Russia because they're asymmetric: a parcel bomb in Russia does not cause the same level of public outcry when the president can bomb a few apartment buildings and get away with it, due to restricted media.