It seems to me that the firing was personal.  For some reason, Trump was angry at Comey.  I don't think it is reasonable to think Trump is so stupid that he actually thought firing Comey would de-escalate the "Russia" story.  Perhaps we will never know the reasons for the firing.  We will never know what Comey said privately to Trump that may have angered him.  In any event, of course, the "Russia" investigation will continue.  Probably for all four years of Trump's term.  Many will not let go of this matter being desperate to find some matter over which they can scream impeach the Donald.  And we wonder why our government is so dysfunctional.