I can't believe I am defending Hillary, but she has a point (I should note that there are still plenty of other reasons to dislike and not trust her). Most presidents, including all of the last 4, get rid of the old ones and appoint new ones when they take office. A US Attorney will typically serve for four years. It is somewhat unusual to get rid of them in mid-term. IIRC, it has only happened 4 other times in the last 28 years.