Trump can’t unilaterally make this type of decision. It would have to go through congress. Announcing you’re buying a scare asset before buying it would be very stupid.
Discussion
It would be stupid to announce his intention of establishing a reserve if his priority is to buy as much coin as possible on the behalf of the US. But if his priority first and foremost is to garner as many votes as possible from the demographic that wants the US to buy as much coin as possible, i’m not sure if it’s really that stupid.