As I said previously, Bonnie Dumanis (and to a lesser extent, Nathan Fletcher) is the establishment candidate for mayor. So its not at all surprising that members of the San Diego political establishment would give her money and support. Lynne Schenk and Murray Galinson fall into that establishment category, and even with Bonnie Dumanis being a Republican, they're going to support her.
Additionally, there is a bit going on behind the scenes. Specifically, it appears that Kehoe is staying out of the Mayor's race (for now), so the sole remaining Democrat is Bob Filner. The Congressman is a tireless campaigner, a brilliant mind, someone who cares deeply about his constituents, and is actually passionate about his job. If Filner becomes mayor, he's going to work his ass off. As a progressive, I'm pretty pumped at the idea of Filner, also a progressive, being mayor.
That said, Filner has a reputation of being prickly. Or, in less polite terms, Filner has a reputation of being an asshole, particularly by his enemies. One particular enemy is Juan Vargas, who ran against Filner in two epic bloodbaths (and one completely disappointing campaign) that left both men scarred for life.* Galinson and Schenk are current and former Vargas supporters, and so its not at all surprising that they are backing Dumanis.
I have no idea if Sessom comes from the Vargas camp or not, but I wouldn't be surprised if she was. As far as her line about Jess Durfee, I find it somewhat surprising that a mayor who has asked for and received the Democratic Party endorsement time and time again doesn't know who the Democratic Party Chair is. In this respect, Lucas over at Two Cathedrals is right.
Nonetheless, for the Democratic Party insiders who haven't been on the lines of the Filner-Vargas war, Bob Filner is their guy. Note that both Kehoe and Frye both slightly backed away from running for mayor when they heard Bob was in. They didn't do that out of fear, they did it out of respect. And not only will the Dem insiders back up Durfee's statement that the endorsement of non-Dems in this race will be punished, they'll cheer him all the way.
And this is a big, big problem for Dumanis. She's gay, she's pro-union, not fiscally conservative, and completely out of touch with the Republican Party. With the DeMaio in the race, Dumanis' only hope is gather enough support from Democrats and independents. But if Filner is in the race, and is strongly supported by Democrats, Dumanis is toast. She knows that, Bob knows that, and that's why the endorsement thing is a big issue.
*I'm not even remotely joking about this, and no I can't tell you how I know.