Hi there Bubbles, He can tell Muller to stop.  It would be really bad, and look even worst, but he in fact, lawfully he can fire him.  If Trump goes down for obstruction so should Comey and he should lose his law license as he would have made a an ethical breach of monumental proportion for not reporting it up the chain ASAP.  I would like to know how Trump has yelled Fire in a Theater or done anything unconstitutional.  Look, President Trump has done some silly things but nothing that is really bad.  Talking to the Russians, Canadians, Indians, English, Estonians and Jordanians and sharing classified intel on matters such as ISIS and such things that you and I have no business or right knowing is a good thing.  If you are unable to see the forest through the trees I cannot help you.  Wishing you a great weekend.

Cheers friend~