No, this one is all on the U.S.
I am not comfortable drawing any statistical inference from a cyclic data set until I have something like 30 cycles to work with (100 is better, at 500 I can be specific). The NSIDC data is a rare bird - a quality data set with detailed global coverage covering nearly 40 years. Even so, I would not yet hazard a guess whether the declining trend is linear or just what. If I do 30 year cuts at five year intervals, in two more years I will have only three NSIDC data points to work with . . . .
The current administration can draw a line under NSIDC data with a stroke of a pen. It would have to actively support the program to get the next set of sensors on orbit - something that so far as I know is not currently programmed - in order for us to say not only is ice declining, but state with any confidence how it is declining, on the basis of 50-60 years of data. It hurts that, just as NASA/Icebridge is beginning to do detailed work to validate and improve understanding of the fine structure of satellite measurements, the proposed budget would essentially end the whole line of research (that is to say polar ice in it's entirety, not just Icebridge specifically).
There is no good way to splice AMSR2 back to NSIDC data. If JAXA keeps sensors up, and can make them directly comparable across generations, we are still looking at 30 years before we can say things about JAXA data that we can today about NSIDC trends.
It is very probable that by the time we can say with confidence the rate of JAXA area/extent drop is linear, increasing, or decreasing, there will no longer be summer ice to measure and the question will be moot.
Human activities to influence the trend are, as I believe you are saying, another matter. The U.S. was long the largest economy in the world. It is now number three, and despite the bluster, there is no sign the trend of its influence will turn around any time soon. The current administration is on a path to last at best four years and in any case, the rest of the world is continually gaining leverage to influence U.S. behavior. There is hope (but way off topic here).