I think the current situation with NATO is different than the alliances of WWII.
Lets say that Russia invades Europe. If NATO doesn't respond, then the alliance is null and everybody fights for themselves. Which isn't a good situation to be in, given that countries in Europe don't have the capacity to take on Russia by themselves, I mean given our experience from WWII.
We learn from mistakes and history teaches us that an invader will not be conservative about where to draw the line. The world also thought Germany will stop at Czechoslovakia too and they were wrong.
And nowadays we also have nuclear weapons and during the Cold War the presence of NATO troops in an area was enough to deter the advancement of the soviets and vice versa.
Russia can't (and doesn't want to) really "invade Europe". What they can do is effectively bring small parts of the baltics, perhaps a whole baltic state as a maximum, under the russian umbrella, and e.g. replace the government with a russian friendly one, put a military base or two there etc.
They don't have the resources to hold "unfriendly territory" (their economy is bad enough as it is). So what would happen is things that would confuse the international community. Fraudulent elections. Violence in the streets. Politicians and journalists murdered. And then suddenly that state is Russian friendly i.e. "effectively part of Russia".
What happened? Was it war? Was someone invaded? When? Is Article V invokable? Is Article V even written to cope with such a scenario? What if there was a proper democratic turn towards Russia? It's Ukraine all over again.
We can't expect (even with Trump) to see massive use of force just because a few green men are shouting in a square somewhere. Or because an election seems dubious in Riga. But wait long enough, and it's fait accompli. The Russian friendly government installed will reject any offerings of military help, because now you are asking the russians whether they want the russians out of the Baltics!
This is why the only working deterrent is to simply have massive Nato ground forces permanently in the Baltics. When you get Maidan square like things going on, you need OECD and NATO people on the ground already. They won't be admitted after a while.
Article V should be explicitly clarified to include e.g. holding elections without a long enough notice, and doing it without OECD and NATO oversight.
Lets say that Russia invades Europe. If NATO doesn't respond, then the alliance is null and everybody fights for themselves. Which isn't a good situation to be in, given that countries in Europe don't have the capacity to take on Russia by themselves, I mean given our experience from WWII.
We learn from mistakes and history teaches us that an invader will not be conservative about where to draw the line. The world also thought Germany will stop at Czechoslovakia too and they were wrong.
And nowadays we also have nuclear weapons and during the Cold War the presence of NATO troops in an area was enough to deter the advancement of the soviets and vice versa.