SAN FRANCISCO (AP) — The Democratic presidential field is shrinking but not quickly enough to ward off the prospect of a long, bruising fight for the nomination.

Three candidates dropped out of the race over the last two weeks, and several others could soon follow. What remains will be a historically large, double-digit roster that includes an unusually high number of strong campaigns poised to go deep into the primary season plus a gaggle of others doing just enough to survive with less than six months before the Iowa caucuses.

It's a scenario — on display Friday, as more than a dozen candida...