Make no mistake, Russia does not have the ability to fight a world war with Europe, so would requires allies. Basically, China. And that would be enough to set the US off.
Trump talks a lot, too much, trying to use bullying and threats to effect changes he wants to see. But at any hint of war with Europe, we'd be right there with them.
I don't worry about any of this now personally, because Putin is more calculating than that. And even if he's gone completely bonkers, Jinping is way too careful to be openly associated with them at this point.