As to an attack on Poland, yes I believe the Europeans would fight. My opinion of the Russian Army is no better than my opinion of the old Red Army. The Poles could probably defeat them on their own, but in combination with us they surely would.
How much would other countries contribute? As usual, the Brits would be there. I'm not sure the others could do much as they've drawn down their militaries so much since the Cold War.
That's the rub, isn't it. How many fledgling democracies are we willing to give up to appease Russia? It really is the cold war all over again. Keep throwing others to the bear so he doesn't eat you.
I understand the political, military and economic reasons why we might back down, especially concidering our 'allies' on the european continent have shown no backbone against real threats.
But it doesn't stop me from feeling badly for the millions in countries that for the first time in generations had a chance to control their own destinies and now face the return of the iron fist.