This is hilarious mcfarm!!

 Of course the explanation for why this happened?

Is this:

However, for those that say that Biden has not lost any cognitive ability.............the proof that he has lost a great deal of cognitive ability couldn't be more obvious...................if you are being honest.

 https://www.youtube.com/watch?v=0_v00iGJCLY

https://www.youtube.com/watch?v=D1j0FS0Z6ho

https://www.foxnews.com/politics/biden-court-packing-stance-1983-bonehead-idea

Can he perform the duties of being president?

Sure doesn't look like it. 

He once was a gifted, high energy, quick thinking speaker that rarely made gaffes. The links above prove it. He told lies and got in trouble for it(had to withdraw from the presidential race after getting busted  on several lies) but they were intentional, not gaffes back then.