As others have indicated, Trump is making serious in-roads into the African American voter block. Hillary wanted to fight back and decided that Obama was asked to produce a birth certificate just because he is black. Therefore Trump is racist, therefore this old issue needed to be resurrected.
For the record:
The Dems questioned Eisenhower’s birth.
The Dems questioned McCain’s birth
The Republicans (esp. Trump) questioned Cruz’s birth
But questioning Obama???? It must be all about the skin color!
Eisenhower?