This is basically fourth-hand info, so take it with a grain of salt: but what I've heard boils down to this:
The Democratic Party, in its capacity as an actual political organizing apparatus (not an identity/platform), never really recovered from the broad shift in influence from labor to finance in the late '70s/early '80s. It has thus fallen back to relying heavily on a strained ad-hoc network of political machines built by various "rock star" Democrats. That's why the party loosely realigned around "third way" / "blue dog" Democrats in the '90s; it's not that there was some transcendent soul-searching about principles, it's that people like Bill Clinton and Evan Bayh were supported by campaign apparatus that won tough elections. More broadly, this has led to an arguably pathological degree of deference among Democrats to any org that has a track record of winning elections. And whatever faults Feinstein's political machine has, it has that track record.
The Democratic Party, in its capacity as an actual political organizing apparatus (not an identity/platform), never really recovered from the broad shift in influence from labor to finance in the late '70s/early '80s. It has thus fallen back to relying heavily on a strained ad-hoc network of political machines built by various "rock star" Democrats. That's why the party loosely realigned around "third way" / "blue dog" Democrats in the '90s; it's not that there was some transcendent soul-searching about principles, it's that people like Bill Clinton and Evan Bayh were supported by campaign apparatus that won tough elections. More broadly, this has led to an arguably pathological degree of deference among Democrats to any org that has a track record of winning elections. And whatever faults Feinstein's political machine has, it has that track record.