Bob Filner’s days as mayor of San Diego are numbered. Here’s why.

San Diego Mayor Bob Filner is not resigning. He's made that very clear publicly.

In reality though, the Congressman-turned-mayor, who faces sexual harassment allegations and calls for him to step down, almost certainly can't survive for much longer.

"It's difficult for me to see how Filner can actually govern the second-largest city in the largest state in such distracting and debilitating circumstances with no base of support, no spouse or significant other to attest to his good qualities, no real friends, and no loyalty from his own party members," said veteran California Democratic strategist Garry South.

Yeah, that pretty much sums it up.

In case you're just tuning in to the Filner saga, welcome. Here's where things stand.

Filner, who served in Congress from 1993 to 2012, faces allegations that he sexually harassed multiple women. Filner and his fiancee have split up, and she says he "recently began texting other women sexually explicit messages and setting up dates while in my presence and within my line of vision." Former Filner supporters have called for his resignation, and he faces a growing recall effort. And the "Filner headlock" has become part of the California political conversation.

Despite all that, Filner says he will not resign. He apologized last week, saying he has "failed to fully respect the women who work for me and with me." But he said Monday that he has no plans to step down, adding: "I do not believe I am guilty of sexual harassment, and I believe a full presentation of the facts will vindicate me."

Filner hasn't been charged with anything by authorities. And the women who have made the accusations have not made their identities known. But the level of resistance Filner is facing would be enough to force many pols from office. Unlike the case of former President Bill Clinton, South noted, the pressure on Filner to exit is coming from his own Democratic Party. This is not a partisan witch hunt.

Pressure from allies has left Filner on an island. And this story will continue to overshadow anything else Filner does, which will make it near impossible for him to move on.

In short: Filner may be resolute against the prospect of resigning now, but it may not be much longer before he changes his tune.