The elderly man with a poor memory could never be used by a target or defendant in a federal case as a defense.
They have allowed demented and the mentally regarded to stand trial and appear in court.
If there was such a question as to his ability to appear in front of a jury, the DOJ needs to obtain a neurological and psychiatric consultation for his fitness to stand trial.
You don’t dismiss an investigation because the target is impaired. At the very least a determination is made as to the merits of the investigation and whether there’s enough evidence for indictments. Then, determine whether defendant can be put on stand.
But it CAN be used to oust him from power!