These scores started dropping as soon as we moved away from phonics to the now mostly debunked Whole Language system where kids are taught to guess words based on context rather than learning how to sound them out. There is a lot more to it than that, but that is the 100,000ft view. Of course if you follow the money on how the Whole Language fad started it was all about kick backs.
Trump is an idiot, but his push at getting rid of the dept. of education, and shipping the funding directly to the states to determine how it's spent might be the best way of pushing back on the forced implementation of things like Whole Language since a central entity can't be bought and then force wholesale adoption at the gunpoint of withheld funding.
#1 quite the leap from the topic to your post.