Here's how Higdon becomes the in-charge guy for the Mueller investigation:

1) Attorney General - Jeff Sessions -recused

2) Deputy Attorney General - Rod Rosenstein

3) Associate Attorney General - Vacant - Jessie Panuccio acting

4) US Attorney for Eastern District of Virginia - Vacant - Tracy Doherty-McCormick acting

5) US Attorney for Eastern District of NC - Robert Higdon

6) Us Attorney for Northern District of Texas - Erin Nealy Cox

>>1513834

Part of the Succession order is that no one in an "acting" capacity can serve as Attorney General, so the flow would continue to the next person in line.

Higdon is in position 5 in the succession flow.