So it’s not a stretch to think that once a Russian tank would cross into Poland it would be met with immediate lethal force.
[0] https://news.yahoo.com/downing-russia-jet-stab-back-putin-13...
It was one jet, and it wasn't fighter jet, but assault jet, it didn't carry any AA missiles and couldn't defend himself.
The line is the borders of the NATO countries. I don’t think it’s particularly controversial that if someone drove a tank into Poland offensively it would be promptly incinerated.
By clearly defining it, it makes it less likely to escalate to accidental MAD. We know the line, Russia knows the line. And they know the potential consequences should they choose to cross it.
On the other hand Russia has recently been opening their doctrine to allow nuclear strikes in response to conventional attacks. Further they threaten nuclear responses. They're intentionally blurring the lines because they feel they can get away shenanigans in the confusion.
If Russia launches nukes - there's nuclear response, but at that point it's not really "escalation", just extended suicide by Russia.
Anything else would put you at a severe disadvantage.
The goal here is to prevent one invasion, not start another one.
But there ought to be enough fighters in Europe to swat anything flying in Ukraine out of the sky.
It will or there will be no NATO. It's the whole point. Certainly Poland won't just give up not to make other NATO countries angry.
And no, I don't think Putin is going to try to conquer Europe (at least I hope he's not that mad). I just wonder where the line for action is and whether it's "touching NATO soil" as you imply or something much more vague and flexible once the prospect of actual war is real.