Russia still the greatest threat to United States? bigger threat than China?

Russia's population will decline by 5 million by 2050, which is a lot since populations are to grow if a country seeks prosperity and desires to care for the elderly. Demographics account for the fall of the Inca Empire and the Roman Empire. Nuclear weapons do not do anything in society, except built a threat. It is almost impossible (if not impossible) for a country to achieve nuclear superiority. Nations like Iran, that are not rational, do not abide by the same principles as russia. Radical Islamic nations do not care as much about surviving as opposed to more rational actors. Russia has never won a major war without allied support. They have only expanded into mainly eastern Asia and kept theses territories successfully. These were mainly weaker nations or territories that were not highly occupied. Russia, aside from their nuclear capabilities, show no huge threat to the US. China, on the other hand, has steady population growth and they have the numbers to create a huge army...this is something Russia likely never had.