First, anyone Obama could have appointed is an upgrade over Holder. I realize that’s a pretty low bar to pass, but after nearly six years of Holder the bar has just been elevated even if only a few inches. Given that Obama wasn’t going to appoint a conservative Republican, this was probably the least bad choice he could have made.
Second, former New York City Mayor Rudy Giuliani has praised Lynch’s professionalism. If anyone is knowledgeable about New York prosecutors it would be Giuliani. If Lynch had engaged in dubious behavior in her office, Giuliani would surely sound the alarm.