@revelette3,
I doubt that she meant that literally. However there is a stark difference between the energy, concentration and mental acuity evidenced by Sanders and Biden in their public remarks. Sanders appears to be a skilled debater, able to deal with aggressive questioning and explain the reasoning behind his political beliefs. Biden is clearly not.
I don't agree at all with the arguments Sanders presents. For example, he justifies his health care programs by noting some, possibly questionable, statistics about total costs and spending for health care, noting that there must be some way to achieve the equality he seeks, but without making any effort at all to explain how such an outcome could actually be achieved in the real world, beset as it is with the complexities of human nature and human behavior. This, of course is the key universal element of socialist delusion. Human nature simply does not conform to their naïve and unrealistic expectations. Worthwhile ideas require a good deal more than just wishful good intentions. That, indeed, is one of the central lessons of human history.
Biden by contrast usually sticks to a prepared script ; speaks in short, half-completed, thought bursts; and avoids extended dialogue on complex issues. In addition he has a long-standing habit of salting his remarks with various gaffes, awkward metaphors and illogical observations.