War is fundamentally different now than it was at the beginning of WW2. A nuclear superpower cannot be invaded. You can poke the bear A LOT, but basically everyone recognizes that a ground invasion is crossing a red line.

That's the purpose of NATO. In exchange for giving up some autonomy to the US (letting the USA build military bases in your territory, not acting overtly against our interests), and paying us for our fancy weapons, NATO members get the immeasurably valuable power of a nuclear red line border, and protection by the most powerful military the world has ever seen. It's a very, very good deal, and the most stabilizing force in history.

Given the NATO membership of most of Europe, the only wars possible in Europe are small, regional conflicts between non-member states.

Fair point. But if you want to use that analogy, maybe you are also willing to admit that the might of the Wehrmacht accomplished substantially more than getting bogged down about 100km beyond their initial borders two years into the conflict?

Besides an open military invasion (hopefully improbable), I'm afraid of slowly tilting and influencing border states (Slovakia, Hungary) to lean towards Russia, with maybe some future economic extortion, or in the very extreme case, staging an election/referendum to leave EU/NATO.

How did that work out for the Germans?

Someone was always wrong about something similar in the past.

That proves nothing about the present.