Russia, obviously. But remember, this war is in Europe — Poland, Latvia, Lithuania, Estonia, and Finland all consider the territorial aims of Russia to be existential threats. The reason so many former soviet countries (like Ukraine) want into NATO is fearing Russia as an existential threat.

Biden was, I think, was afraid of escalation, of Russian nukes.

Trump and Putin both think in terms that could be phrased as "great powers set the rules, everyone else is an NPC". Both are going to continue to be confused that Europe doing exactly what Trump is telling them to do — increasing military spending — is going to result in a Europe that has no strings binding it to the USA.