If you are interested in a more detailed portrait of the shifts happening, this book is excellent. If the US loses its technological advantage and its reserve currency status, it is very difficult to know what will happen. https://www.amazon.com/Shadows-American-Century-Decline-Disp... China's biggest problem will be demographics, second only to their political system. US will likely due to tax / deficit issues, not…
Or you could see it as being like the USSR which drove itself into the ground by spending everyone's money (trying to keep up with the US) faster than everyone could create it.
Tax/deficit problems can not be considered just tax problems or just spending problems because the amount of input is not meaningful except in relation to the amount of output. It's like how diet and exercise need to be considered together if you want to make a plan for meaningful weight loss. If we stopped playing world police (or just did it less) and made the government gravy train more efficient (i.e. less of a gravy train, which sounds easy but it's actually hard because nobody wants to stop pissing money away on their pet program/subsidy) we could probably have both good social safety nets and less taxes.