When was the last time Trump made birtherism an issue? I don't recall it all during the long campaign. It certainly hasn't been a centerpiece.
It seems to be splashing more mud on those the raise the issue...the media... as more learn it was Obama himself or Hilary's campaign that tried to save a dying 2008 campaign be challenging Obie's American roots and/or actual birth.
Birtherism is a term used by the Left to demonize and shame those who believe that one must satisfy the eligibility requirements under the Constitution to be President. Was Obama a birther when he co-sponsored the Senate resolution on McCain's eligibility? Climate denier is used similarly by the Left to equate those who question man-made global warming to the Holocaust deniers.
Trump used the "birther" issue against Cruz questioning his eligibility and rightfully so. SCOTUS has never offered an opinion on the definition of natural born citizen.