Ukraine

Should they, though? You do realize that results in the entirety of Europe being pitted against Putin's Russia, who is still a nuclear power run by a despot despite their decaying conventional military. The potential mobilization could begin to snowball very, very rapidly. Russia also still has the BRICS alliance behind them to feed them resources, although the cohesiveness of their pacts has yet to be tested. It could turn into a horrifying bloody mess ten times the scale of Ukraine overnight.

NATO actively escalating the situation also plays into Putin's propaganda machine. He has long painted NATO as the aggressor, as NATO being the one who encroached upon Russia's borders. It's effective to drum up nationalistic sentiment. Proving him right would galvanize Russia's population, increase his support, and only further cement his slowly-crumbling political power both domestically and internationally.