This past week, he had three choices when making reference to when Michelle Obama gave her "elegant" speech; he got it wrong twice.
That leads us to what could be the correct psychological diagnosis. Generally, there are 15 common psychological defense mechanisms people employ to deal with uncomfortable realities. One of them is known as Dissociation, which is what I believe Mr. Biden may be afflicted with.
Via Psych Central:
Dissociation is when a person loses track of time and/or person, and instead finds another representation of their self in order to continue in the moment. A person who dissociates often loses track of time or themselves and their usual thought processes and memories. People who have a history of any kind of childhood abuse often suffer from some form of dissociation. In extreme cases, dissociation can lead to a person believing they have multiple selves (“multiple personality disorder”). People who use dissociation often have a disconnected view of themselves in their world. Time and their own self-image may not flow continuously, as it does for most people. In this manner, a person who dissociates can “disconnect” from the real world for a time, and live in a different world that is not cluttered with thoughts, feelings or memories that are unbearable.Pretty much nails it: