What are the motifs in Separation of Power by Vince Flynn?

Marriage and understanding is a recurring idea. One plot line of the book details the love affair between Mitch Rapp and Anna Rielly. At the beginning, the narrator presents them as deeply in love, living together in Mitch's house in Maryland and thinking about marriage and kids. Anna has even persuaded Mitch to retire from his dangerous work with the Orion Team. Mitch agrees to this after he has found out who tried to kill him in Germany. With this mind he takes Anna to Milan to both propose to her and to visit the assassin Donatella and find out who hired her to kill Peter Cameron.