I'd say for that specific example (confirming President's official speeches), regular public/private key systems signed by official key published by the White H

I'd say for that specific example (confirming President's official speeches), regular public/private key systems signed by official key published by the White House would work even better. As GP said, you are trying to answer a question: "How do I apply blockchain here". This is never a right question, you should instead be asking: "which technology will allow to solve this problem in the most optimal way according to users".