He is only a place holder. And he knows it in his better moments, he has said "I'm old, I will step down, I'm going to die." The plus of using a demented person is that they are on autopilot a lot and Joe has been making political blather for so long it's natural. They can be tricked. Their family may be ready to let go of them. The downside is that they aren't filtered much any more. Fortunately for the placeholder scheme, he can be isolated a lot because of the dreaded virus.