The same, tired and now very boring old tune. I thought (hoped?) this discussion would cease once the UK had left the EU, after all, what concern is it of ours now? Who cares what the European countries do now? Its up to them. I guess it keeps you warm at night, still raging on and on about this...
Personally I wouldn't give a stuff if they left NATO and went their own way. Actually it would be amusing to see some in America twist and turn over this, especially if the likes of Germany turned around and told them to leave Ramstein.
As for the Russian threat, I sincerely doubt they could trouble nothing more than the odd Baltic state (and what would/could NATO do about this? Not a lot IMO). They certainly wouldn't want to go up against the likes of Poland, especially given their laboured efforts in eastern Ukraine.