In poll after poll jeb bush has at least 60%+ of the country saying they would never vote for him. He'll sink faster than the titanic, we just aren't going to elect another bush so quickly.
I did see one poll with his negatives very high. I have not looked for others. I personally don't think such polls are that meaningful for someone who has not been on the national stage that much.
Still JEB says he is not running which is why I keep looking at midwestern governors. If one has the personality and could get the nomination, he would be a shoe in in the general if he could carry a couple of extra midwestern states that have been very tight the last two elections.