It sounds like Trump is a better communicator, or leader of public opinion, than people gave him credit for. It's not very likely that he wasn't previously aware of the natural born citizen issue. He's starting where the (MSM indoctrinated) public is now, and methodically chipping away at the issue. The difference between being: a citizen; born in the U.S.A.; and natural born citizen is slowly being revealed to the unwashed masses.
He's had a few decades of being a business leader. Part of being a leader in business is **educating** the ill-informed. He's had LOTS of practice at this.
As you pointed out, Trump is chipping away at this. He is educating the public a little bit a time, by giving them milk before meat, and by chip, chip, chipping, he is also keeping this headline news. He's nailing two birds with one stone.
The man is smart! ( Just like he says he is!)