Who is Paul Vandenberg from The Mark of the Assassin: A Novel and what is their importance?

Having known President James Beckwith for forty years, Paul Vandenberg is an opportunist who has "managed" Beckwith, his political career and his wife quite well. With Beckwith's election to the Presidency, Vandenberg is now the White House Chief of Staff, and, from this position, is easily able to control policy and action coming from the White House. Vandenberg himself is making the decisions and then "selling" them to a trusting Beckwith, who believes that Vandenberg truly understands the "pulse" of the nation and the world.