Put yourself in this situation.
You are in a position of importance. Lots of people rely on you. You are supposed to be a leader.
A year before, your son was involved in a questionable event.
People want to know what happened.
Your staff advises you to issue a truthful statement about what happened. One that could not be contradicted later as more information comes out.
You veto that advice, and craft a different statement, word for word. That different statement sets forth a lie about what happened.
Later on, you say that you knew nothing about what happened until the media reported it.
Who me? Did I do that? Fake news! Investigate Hillary! Yes, you got the idea. The “you” in the above scenario is in reality, Donald Trump. Sorry if playing the role of Trump above grossed you out!
But you get the idea. The dude in the White House cannot be trusted farther than an ant could carry him on its shoulders.