The anti-incumbent, anti-establishment sentiment had Jeb doomed from the start. Conservatives see him as they do a Kardashian, as in "Holy crap, there's ANOTHER one! What are they, Kennedys?"
Jeb is running TV ads here in SC in which he's trying to talk fast, trying to be animated and it's because Trump said he has no energy. He is trying to counter that with these tough guy commercials and he's totally out of his element. In eight years as governor of Florida the state was on cruise control. Tourism and high property taxes kept Florida perpetually in the black and he governed before the real estate bust and before these pension obligations got so out of hand.
Having been a politician for so long (first ran for gov. In 1994), he's seen as indicative of what's wrong. I have a feeling his days are numbered.