The first is because he's viewed as unstable, uninformed, chaotic, unqualified, and nuts.
The second is he has no campaign infastructure to speak of and can't compete with her ground strength wise, fund raising wise, or spending wise. If he were a true billionaire like Bloomberg, he could just throw 500 mill of his own money into it. But he doesn't have it. He has a cash strapped, incompetent campaign.
The third is that women, moderates, and Hispanics overwhelmingly reject him, and they are key blocks to winning the general.
In short Nuttie, incompetent, and extreme gets you beat every time.
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