The Clinton campaign has gone after Sanders by trying to plant doubts about his ability to serve as President, due to his health. I don't know about Bernie's health, but I have great concerns about his age.
I have other doubts as well. I ask if someone as far left as he appears to be, could ever win in places like the Midwest and the South. I don't think he has much of a chance. As far as being President is concerned, with all his angry screaming about the inequality in the country and the piracy of big business and corporations (things, which incidentally I agree with), I don't think he would make much headway with a Congress that is likely to be Republican dominated.
Bernie Sanders reminds me of Ralph Nader, the destoyer of Democratic Candidates, and the on of the main reasons that George Bush got into office, and Al Gore lost. Bernie will never win the votes of most people in this country, but like Ralph Nader, whose supporters blissfully believed that they would buck all odds, Bernie's followers will lead us into the pits, but as they do so, they will be cheering wildly. A vote to make him our candidate is the surest way to assure that Donald Trump, or maybe worse yet Ted Cruz will be our President.
Sure, what Sanders preaches makes sense, but the chances of his getting his agenda through congress are exactly null. Even Democrats in Congress may not support his agenda. As far as the health issue is concerned, Bernie is currently 74 years old. That would make him 75 by the time he is inaugurated. If he is lucky enough to get through his first term and was elected a second time, that would make him 83 by the time he left office. I really can't think of someone in his 80's having enough energy to cope with the hostile complexities that surround us these days. The likelihood that he would become non-functional while in office is great, and who we are voting in as Vice-President may next hold the office. Clinton would be 76 by the time she finished her 2 terms – merely 2 years older than Sanders is now.
If the world suddenly turned into a fantasy land, Bernie would be my choice for President. But as things are, I figure that despite some of her faults, faults which the press has so gleefully broadcast, I think she would make an excellent President. I think she has a far better chance of being alive at the end of her 2 terms, and a much better chance of challenging the vicissitudes of the modern world.