Question

what does Whitehurst mean when he says that by the time he speaks with candidates "they've already been extremely vetted"

Answer 1

The term "vetted" means "to make a careful examination," or "to investigate someone thoroughly." It is commonly used to ensure someone is trustworthy for a job. When Whitehurst says that the candidates have already been "extremely vetted," it is implied that the candidates were investigated to a great extent.