Presumably, if they were successful, at some point we Europeans would also go in and start bombing, so it's not like they can actually hope for a true breakthrough or taking Kiev or anything like that.
No, you can't because that would trigger World War 3. Any attack on Russia, by NATO or any European state, would trigger a retaliation from Russia. It would also trigger Russia's military alliance with China and other countries, who would also join the war. This is the reason why NATO or any of the European nation is unwilling to join the war directly, and only helping Ukraine with money, armaments and equipments (which unfortunately isn't enough as Russian economy and military is stronger).
Depending of course, on what you mean by world war three.
Russia will certainly not respond with nuclear weapons, as the EU would similarly respond with nuclear weapons. I don't China and Russia have a defence pact where each has agreed to come to the aid of the other.
Consequently I don't agree at all, and I don't think it's a problem to have war with Russia.
