Let us consider the high level of speculation surrounding the veracity of current polling showing Clinton ahead significantly.  Then let us consider also, in this light, that even with the tampering, they show her only slightly ahead.  They have their own internal polling that is trying to gauge the mood of the electorate to determine what their chances are.  What if what they are seeing is signs of disaster for the Clinton Campaign? 

The Clintons are nothing if not forward-thinking.  The ramifications of a Trump presidency for Hillary Clinton could be sweeping.  A thought that might have crept into her mind might be that he just might keep good on his promise that if he were president, she would be in jail. 

The email investigation being reopened could simply be a foil for just such a situation.  In the event that Hillary loses the race, sometime during the (ahem) "peaceful transition period," either charges will be brought against her of a minor nature for prosecution, or a friendly court will see to it that they are dropped after consideration, preventing a trial on the same grounds.