For much of Ed Lee's first term as Mayor of San Francisco, he enjoyed both the popular support of the public and the financial backing of tech tycoons. Last March, a stunning 65 percent of local voters approved of Lee's handling of the job. Then the Google Bus protests happened, the cost of living kept rising, and evictions hit crisis levels. Within 13 months, Lee's approval rating sunk by 20 points.

The mayor still has a year before his reelection, but tensions only seem to be heightening and his challengers aren't wasting any time. Just today Mark Leno, a popular California state senator, said he is mulling a run against Lee.

Lee's standing around town, for example, took a hit after the city legalized Airbnb earlier this month. Senator Dianne Feinstein encouraged the mayor not to approve the bill, which let Airbnb off the hook for a retroactive tax bill. But Ron Conway and Reid Hoffman, who both invested in Airbnb and donated to Lee's campaign, backed the bill.

As SF Weekly's Joe Eskenazi reports, U.S. Senators rarely swoop in from Washington to chime in on local legislation. But Feinstein was so alarmed by what Airbnb was getting away with, she called the Mayor, "[attempting] to explain to him how this ordinance would eviscerate city zoning rules, deplete already-scarce housing stock, and enable a company that has made a point of not paying its taxes."

When that didn't work, the Senator wrote an op-ed for the Chronicle, warning the Mayor that "this bill will further increase already sky-high rental costs."

Mayor Lee signed the bill anyway.

He looked weak in the face of the prospering tech industry. Voters now know he can't coax $25 million in back hotel taxes, even from a company valued at more than $10 billion.

Even Rose Pak, the Chinatown powerbroker who helped elect Lee with her "Run Ed Run" campaign, is cooling her support of the Mayor. The Chronicle reports Pak and the Mayor "have been drifting apart for months" over Lee's relationship with Ron Conway.

It's no wonder Leno sees an opening. Earlier this week, the Chronicle quoted Leno paraphrasing Feinstein's complaints against Airbnb:

"In one stroke, we have rezoned the whole city," Leno said. "There is a compromise to be found, but this is not it — it's too broad."

Leno is hardly a quixotic challenger. While Lee handily won the mayor's race in 2011, beating a progressive city supervisor by over 19 points, Leno is an undeniably stronger challenger. San Francisco Magazine's Scott Lucas explained the appeal:

Leno could present a tough challenge to Lee. He has cred with both San Francisco's progressive and moderate wings, a strong record in Sacramento, and has already city-wide election several times.

A poll conducted this past April already shows Leno besting Lee by four points. And Senator Feinstein, who previously endorsed Ed Lee, has indicated she would join Leno in fighting to repeal the city's Airbnb law.

To contact the author of this post, please email kevin@valleywag.com.

Image: Anonymous, via VanishingSF