A US carrier group with a marine expeditionary force will be in the top-10 militaries in the world period.
It has more conventional capabilities than most militaries, a stronger air wing than many air forces, and better ground troops than most, not to mention that a carrier group is usually escorted by at least one submarine which have nuclear capabilities.
No other country really has the ability to project power period, Russia can't the Chinese can't, most NATO nations don't have enough supplies for limited engagement and very limited ability to operate even within the local theater (e.g. European forces required US tankers to refuel during Libya, they've also ran out of munitions and jet fuel within the first 3 days of the campaign).
So for the most part I don't see any country with a capability to even remotely threaten US superiority out side of MAD.
Russia is completely limited, it's defacto a land locked country without a warm water port this is why they've tried to invade Korea 3 times since the 19th century. And also why NATO mostly overlooked Crimea because they've understood that's the last redline for Russia.
China well, China doesn't even has a joint command, they've never really went to war any where or conducted any military operations. Their military structure is ripe with corruption and every couple of years they lose one of their chiefs to some political investigation once they decide to take one bribe to many or too few.
Their expenditure per soldier is laughable, and their equipment although getting better is still decades behind the US and they've shown to have very little self reliant R&D capabilities, what they can't buy they steal which never results well.
The US Army is still the best professional Army in the world, while we all like to point and laugh that they mostly recruit white trash and immigrants their officers and senior NCO's hold probably the best toolkit of military education and experience in the world.