For one thing, he’s not supposed to hold a press conference to announce that an investigation is underway. Read the letters from Sessions and Rosenstein outlining the reasons why Comey was fired.
If in fact an investigation was ongoing you would have heard about it because the democrt targets would have been whining to their allies in the press. Silence means no investigation of the Clinton obama scandals. Plus, why would Trump tweet TODAY that he cant understand why clinton is not under investigation. Do you really think DOJ would have kept that a secret from him?
Your defense is merely wishful hoping that sessions is doing his job when all the availble evidence says no.