Numbers do reverse themselves. The first poll was out of complete ignorance. Since then Trump has become a national narrative and the people have seen him for themselves without the MSM filter.
It was just that many folks didn't like him.
As one man said when he spent a few minutes with Trump in Dubuque, "Trump's different in person. He's a regular guy, vy down to earth, even kind of humble."
I think as people get to know the real Trump, they like him.