You’re having trouble writing not because you can’t find the right words, but because you don’t know what you’re trying to say. You don’t have the right facts at hand.
So the solution is to gather more facts. You need to step away from the keyboard, stop trying to write, and do some more reporting: Make phone calls to some new sources, consult new experts, read a relevant book or article. Once you have the facts at hand, the words will come.
Or to put it another way, when you’re writing nonfiction, the words flow from the research. If the words aren’t flowing, usually the problem is the research isn’t there. To say something, you have to have something to say.
Clive Thompson reflects upon the feeling of writer’s block and suggests that the answer is more research. This reminds me of something Amy Burvall once wrote:
In order to connect dots, one must first have the dots