This is why Rachel Brand left
"Rachel Brand, the third-ranking official at the Department of Justice, decided to resign in part because she “feared she would be asked to oversee the Russia investigation.”
The report does not elaborate on which aspects of the probe Brand dreaded taking on, or whether it was merely the prospect of being thrust into one of the highest-pressure jobs in politics that gave her pause. But it suggests that Brand thinks there’s a decent chance that Deputy Attorney General Rod Rosenstein, who currently supervises the investigation, might be fired by President Trump, a move that would leave her in charge."