Awareness.
Trump has the biggest audience in the world.
Him talking about it puts bitcoin on the mind of millions of people who otherwise would not give it a thought.
Discussion
Think his supporters will buy Bitcoin because mentions in a speech??
On mass no.
But some people will be interested.
Maybe they Google it.
Maybe they finally talk to their friend who has been telling them about it for years.
The majority of people need to be told to do something or that something is approved by a person in a position of authority before they will do it themselves.
They need to be given the go ahead before taking action.
Trump might be giving them the nod of legitimacy they need.