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Even if she tried (I doubt she would), Hillary is despised even by a good percentage of their own party, so it would be very irresponsible of her and the people in the party to allow her to take the place of Biden, it would be again a defeat to her history, the public image she gives is bad.
There are people who are better qualified and younger than her who would be a good president.
There are people talking about Bernie Sanders, but that is not realistic. The establishment would never allow someone as leftist as Bernie to get a chance to get the presidency of the United States, that is why he lost his chance to face Trump back in 2016. Had he been more like the typical capitalist and pro-establishment democrat, he would have faced Trump back in the day.