This won't harm Trump at all. His backers know exactly who he is and don't care about any of his gaffs or "shortcomings." If they were making their decision to support this man on policy and competence, Trump would have never even become the Republican candidate. This news surprises no one on either side. I actually think his comments about 2nd amendment people etc. are way worse than this. Trump can literally say and do anything, and it has little effect on his success. Any other candidate in the history of our country would have been buried months ago.
His base wouldn't care, but what about the undecided voters he need to convince to beat Hillary?