What is Joe Biden struggling with in the opening pages of the novel, Hope Never Dies: An Obama Biden Mystery?

As the novel begins, Joe is struggling with feelings of emptiness, infirmity, and abandonment. To be specific, he feels emptiness because his days are no longer filled with the activities and responsibilities of a political life, and experiences infirmity because he feels his body is not as able or as fit as it used to be. Finally, he feels abandoned because he it seems to him like the busy, popular, globe-trotting Barack has forgotten their friendship, leaving him behind for the world and lifestyle of a celebrity politician.