I'm so old I remember when the wise old men of Washington spent their days fulminating about Janet Reno's constant need to "prove her independence," which generally required her to appoint an independent counsel or special prosecutor on days ending in 'y.'
Whatever the merits of all of those investigations, the principle was correct. The top dog at the DOJ needs to not think of him/herself as the president's personal lawyer, and Democrats should make independence a necessary condition for confirmation.
Sadly, I expect "a good man who Joe Lieberman has a great deal of respect for" will probably be the sole qualification.