The media had hatched up this plan to ambush Trump about the Birther issue and try to tie it to racism, which they would then pin on Trump. Trump squashed their plan like a bug. By saying there was no foreign birth, Trump took steam out of their sails. By charging that the Birther issue came from the 2008 Hillary campaign, that threw egg on their face. They will deny that it was the Clinton campaign and say that it was from unrelated operatives. However, people are finding the Birther charges on Clinton campaign emails.
The foreign birth thing got started way back in 1991 when Barak Hussein himself claimed he was born in Kenya in print.