Let's take this step by step....
First of all, I'm surprised that this sort of goofy war is something you have compared to WWII, my friend. America entered WWII because Japan attacked them (surface level) and on a deeper level because they were still on a forward moment with Christianity mostly driving the behavior of soldiers and commanders alike. That moment is long gone. They recognised an Evil that was not profitable or beneficial for the world long term. They may have recognised that Hitler's Germany had started far away from that spirit of Christianity and also that it was overt Chad worship of themselves. I believe they entered the war cause they suspected this was wrong on some level. Also, this reshaping of the European countries was brought about by Germany invading so many other European lands by force. Ukraine is nothing like what France was, or what the U.K. was, or what Poland was. I don't think Russia really represents a threat to the U.S. IF the U.S. is making the right moves. Whereas pre-WWII and nuclear weapons it's impossible to say what Japan and Germany were going to consider and how far they were going to go. WWII needed to happen. Plain and simple. Defending the criminal stae of Ukraine and with people's lives and money is not at all worth the gains for the Western world. In fact it's seemingly causing more chaos than good for everyone involved. There is a chance I could be wrong, but all signs point to this ending badly, whereas it impossible to know how Putin would have reacted had the U.S. Dems been nice and moreover had there been solidarity among political parties in the US. When the U.S. appears strong and reasonable, Putin would not be so unreasonable. It seems as though the control room of this War is Democrate) Liberals and putting Putin in his place is some sort of power obsession they have with further demolishing the idea right wingers have of anyone like Trump from rising in America.
I don't know if that's completely true. Maybe if the U.S. was reasonable and the EU were reasonable, he would not. Maybe he just does want Ukraine back in the fold. If he really started country hopping AFTER taking Ukraine, then I'd say fine, there is reason to go to war with him. This would still not hurt the U.S./U.K until much later, so there would be plenty of time to act against him. Having several shitty territories is not goin to make Putin's Russia a match for Western Europe and America together. But now we will never know because we started supporting this idiot Zelensky. Too late.
I feel like this would be the likely scenario. Unless he had some super agreements with China/NK/Iran for world domination, then it would have likely stopped there.
Again I'm not saying I'm absolutely certain, but more and more it's appearing like a very bad decision to plunge America into more problems by supporting Ukraine. I think we all knew this was bound to happen the ways things in the U.S. are going. This is the end of Western civilization's prosperity in every single way.