Hillary had too much of a history, even before her term as SoS. Her SoS was not very good, either. And no amount of face lifts and air brushing can change the fact that she is an elder.
Both parties should review their nominees of the last two decades:
1992 Old Bush vs Young Clinton
1996 Old Dole vs still youthful Clinton
2000 draw, age wise
2004 Old Kerry vs still youthful Bush
2008 Old McCain vs youthful Obama
2012 Aging Romney vs still youthful Obama
[Winners in bold]
Notice a pattern?
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Some have been pushing Gore to run again. Gore's problem is too many videoes of him 'gone wild and crazy' and his age. He, too, is no longer one of the youthfuls.