If this were done by the RNC it would be a decent ad. For NRA, not so much.
First, it does not touch upon gun rights at all. Second, NRA is already widely seen as being too tight with the Republicans. Bringing up a non-gun issue reinforces that.
The Donald’s support for 2A is questionable at best so it is understandable that NRA can’t highlight that. However, they could at least try to make the argument that he would make better judicial picks or sign the reciprocity bill.