Ahhh, this old trope. Fork it - trivial to do when you have consensus.
They
- have the data of yesterday
- have backups of the data of yesterday
- are going to write today's data on top of it to continue the chain
(insert magic here)
- somehow we are super sure, tomorrow, that today's data has not been tampered with
If somebody can shine some light on the magic part, I'm interested
The point is that if the hashes of the blocks are published, you can't later go back and tamper with that data.
You don't have to guess, that's exactly what the headline says: "...over fears of national security leaks". And several times in the body of the article.
Why doesn't the Trump admin open up it's data to inspection by European, Chinese, Russian etc auditors? What does it have to fear?