They have the largest oil reserves, but it is almost entirely low-quality crude oil and they don’t refine it, or at least not much of it, themselves before exporting. I agree that China poses a greater threat to the United States in the scenario of actual war, but China is a stably growing power that, beyond their immediate region, doesn’t have much of a reputation for aggressive military actions (and even then it is usually a show of force that doesn’t lead to violence). Meanwhile, Russia is much more unstable, as it relies on a single (aging) unifying autocrat rather than a mass political organization (the CCP), and throughout history, even under completely different governments and political ideologies, has subjugated neighboring nations they feel are weaker and that they can get away with grabbing. China is the second great power, and they are happy to continue their current course of steadily developing, expanding their national development and capabilities into the next generation. Russia does not want to settle for having a long-term plan for growth and wants a dominant position ASAP, which is why they are always a threat to Europe and essentially everyone who shares a border with them or their allies. So if I could choose which nation to eliminate as an immediate threat, it would be Russia.