First, a sidebar thought — isn't it a bit presumptuous to be writing this? Yes, I think Bernie may be throwing in the towel before the end of the primary season, but that's me prognosticating, not opining. And, beyond that, I'm not Texas' major left-of-center opinion magazine.
Second, as I Tweeted Hooks, the "if not Clinton, who" issue shows deeper Democratic Party issues which Sanders is exposing.
A. Biden? He would have a fair amount of the same neoliberal fiscal baggage, and Iraq War baggage (not that Bernie is totally enlightened on foreign policy himself) as Clinton.
B. Dem governors? Please. Name me one after Geriatric Brown (three and a half years older than Sanders). Andrew Cuomo? A hack mired in growing scandal. John Hickenlooper? A neoliberal squish outside of tepid support for pot. Others are blander yet. Former governor Brian Schweitzer could have run outside the Israel box that both Clinton and Sanders are in, and as an "outsider" (and would have gotten my support over Clinton, even with his anti-environmental baggage) but he opted not to run.
One person in a comment back to me listed Minnesota's Mark Dayton. He might be very good on the two hot-button social issues, and OK overall. But, he refused to run for Senate re-election because he hated Washington. He's nine months older than Clinton, which would make him almost as old in 2020 as Sanders is now. (Sidebar: Yes, age is a relevant question about Sanders. Clinton's too old herself to bring it up, though.)
C. Dem senators? Really? Cory Booker might be charismatic, but he's very much a shadow Obama 2.0. From a political perspective, for me, Elizabeth Warren would definitely get my support. Other than that, Sheldon Whitehouse, Sherrod Brown and Ed Markey are the only ones I even might consider — and, of course, that would be just for the Democratic primaries, not the general.
Generally, there's not a creative thinker in that mix, and there's not a lot of people under 60 in that mix.
The problem goes deeper than that. Per a piece I did a couple of weeks about Clintonistas' shit not stinking, the Democrats who responded to a Carly Fiorina attack on Hillary Clinton, and the shallowness of the levels of defense they were above to muster, shows just how weak the party is.