The Chief Executive has the power to fire is FBI director for whatever reason. And it's not unlawful for him to use such power.
Alan Dershowitz: Trump did not obstruct justice in firing James Comey http://www.washingtonexaminer.com/alan-dershowitz-trump-did-not-obstruct-justice-in-firing-james-comey/article/2622875
Yes..it can be
Mark this post. There is a reason Mueller wants docs..like the original one that mcghan kept in a safe.
The only question is whether mueller would leave it to congress or make the Jaworski SCOTUS argument..if he finds evidence of obstruction.