"Either he does run again ... Bill Clinton was actually at a similar rate and he went on to win re-election ... most people would agree Biden is not Bill Clinton but theoretically it's possible," Ms Gada told Sky News host Andrew Bolt.

"The second scenario is he finishes out his term and then steps aside and then other people from the Democrat bench vie for the job.

"And then the third scenario ... is that he doesn't even finish out this term and potentially he steps aside after the midterm elections coming up in November.

"Which paves the way for Kamala Harris to take that top job and then vie for election and that sets up a whole different scenario we have seen in US history but it makes a lot of people very nervous."