To our reader from Iowa who wants to know how tonight affects 2020: I think it depends a lot on what happens. If Beto wins, I don’t expect him to be running for president in the first few months of his Senate tenure. If he loses by more than 10, I think that weakens his rationale for a candidacy. If the Dems somehow don’t win control of the House, I think that makes the case stronger for an outsider to run in 2020 and save the party. That could be Michael Bloomberg, or Michael Avenatti, or Oprah, or all of them. It would also make the case for running Biden as a kind of electable savior.
But if things go as expected (Dem win in House, loss in Senate), I would expect the field to be generally what it is now: a bunch of fresher figures in the Democratic Party (Booker, Harris and Warren are probably the leading three of that group), one or both of the two older, well-known figures in the party (Sanders or Biden) and then a lot of other people.