He took the job precisely to cover his crimes,that’s why he is going to indict Manafort,the best excuse he has for listening in on his phone conversations at Trump Tower.
All the other unmasking had to take place to find out the scope of Trumps associates.
It could also explain Sessions actions,saying he is not going to investigate deep State corruption,or Hillary,we are being sold a bill of goods
BINGO! I've been saying the same....and only adding Mueller also wants to destroy as much evidence of his own criminality as he can along with covering-up Comrade Hellry's own treasonous crimes.