Both challenge the US from various angles: military, economics, culture, education etc.
US is not a singular power, as well. It is the leader of the Atlantic Pact and an amalgamation of the Western hegemony.
China is not a singular power, as well. Although not as institutionalized as the Atlantic Pact, China and Russia represent a new alternative historical bloc to the US-led Western hegemony.
So, I would say, in terms of real challenge, a China-Russia bloc is the most fundamental challenge the US faces in terms of the sustainability of its bloody grip on the world. That's the reason the US wages two silent wars on two fronts: One is with Russia and the other with China.
The rest is simply details or pieces on the board.
That has not been entirely negative development, I think. The way the US panicked and how they watered down the number of refugees they promised to take from Syria&Iraq on the aftermath of Paris terror attacks must have taught Europe a practical lesson in the long run.
Do not get involved in grand strategies with the US, betting on the lives of other people, because, when the knife touches the nerve a bit, the US will simply shroud in its isolationism and let the Europe deal with the repercussions of ill-advised policies.
Excellent points.
Individually, Russia and China are not powerful enough to take on the US, but Russia and China combined would have all the necessary things to fully challenge the US such as:
Large land area.
Large population.
Large workforce.
Abundant natural resources (energy, metals, agriculture).
Large nuclear arsenal.
Large standing army.
Advanced conventional military weaponary (fighters jets, strategic bombers, strategic air transport, attack helicopters, transport helicopters, destroyers, frigates, conventional submarines, nuclear attack submarines, aircraft carrier, LPD, etc).
Advanced space program (satellites, launch facilities, manned, space station).
Satellite navigation system (GLONASS, Beidou).
Large and advanced missile arsenal (ICBM, IRBM, MRBM, SRBM, cruise missiles launched from land, air, sea and subsea).
Advanced nuclear ballistic submarines.
Advanced strategic bombers.
Advanced air and missile defences.
Advanced intelligence and counter intelligence.
Large economy.
Large trading nation.
Large investor.
Large savings pool.
Large consumer market.
Large industrial/manufacturing base.
Large service sector.
Large foreign exchange reserves.
Large gold reserves.
Large creditor nation.
Large stock market.
Large bond market.
Large government budget revenue.
Large government budget.
Highly educated population.
Large number of scientists.
Large number of engineers.
Large automobile producer.
Large shipbuilder.
Advanced technical knowledge on everything.
Advanced technologies in various industries (transportation, energy, medical, electronics, IT, etc)
Fastest supercomputer.
Large R&D budget.
Large military spending.
Large weapons exporter.
Ability to build large scale infrastructure rapidly.
Russia has things China wants, China has things Russia wants. If Russia and China combined, that will be a superpower combination capable of taking on anyone.
