Times have changed, King's Defense is no longer the CIA's good partner, nor the Pentagon's collaborator.
King's Defense is now the rat that everyone shouts at and beats when it crosses the street.
John is a weakness, a soft spot, which he himself knows, Gao Guang knows, and Andy knows too.
So Andy keeps a close watch on John because he knows that finding John basically means finding Gao Guang; and even if he can't track down Gao Guang through John, he can use John as a hostage to blackmail Gao Guang.
But to be clear, the way Andy threatens Gao Guang with John in custody is not like in the movies, where a gun is held to John's head, demanding Gao Guang to lay down his arms and surrender obediently.
No one is that foolish. Gao Guang won't lay down his weapons, so neither will Andy threaten Gao Guang in that way.
