Why is Michael Goldberg under the care of the Secret Service in the novel, Along Came a Spider?

Michael Goldberg is the son of the Secretary of the Treasury and a good friend of Maggie Rose Dunne's. The Goldberg's believed they would never have children, so when Michael came around they saw him as a miracle baby. Michael was a blue baby and has had health problems ever since, including a heart problem that leaves him tired during times of normal exertion. Michael is under the care of the Secret Service because of threats made against his father.