A more skilled and savvy politician than Clinton could and would have buried Trump months ago. A more charismatic, popular or likeable Democratic standard-bearer could now be awaiting electoral coronation.
She's been a weak candidate. Nothing to do with her sex (stand down, ladies). If she'd been facing Bush or even Rubio with a middle-class tax cut, she'd be in deep trouble. Her record of flip-flops (remember gay marriage? TPP?) and her refusal to put forth any really serious policy stances (her site is filled with generalizations and stereotypes; gotta keep that flexibility) condemn her to many.