FBI checking this out isn't going to exonerate her. All that will happen if they say they can't find wrongdoing is it being reframed as the "Democratic Bureaucrats at FBI Shutting Down The Investigation."
Like Benghazi, the narrative will be Retrial Until Proven Guilty.
That might be enough of an explanation for Republicans and Republican-leaning independents who have an axe to grind against her, for whom no exoneration is ever possible.
But don't you think those who are truly independents might be more inclined to accept the verdict, should it come?