>Why is this relevant?
>Provides supportable grounds for?
Rosenstein gave Mueller his marching orders. If Rosenstein is impeached and removed, the person who replaces him could re-examine Mueller's appointment letter, decide it's too vague, and issue a new one that clearly circumscribes the scope of Mueller's task.
"You are limited to finding only direct Russian collusion with Trump. Have you found any? No? Then you're done."