SACRAMENTO — Gov. Gavin Newsom on Monday apologized for what he called “a bad mistake” in attending a birthday party that broke the very rules that he has been preaching to slow the spread of the coronavirus.

He has suffered severe political backlash since it surfaced Friday that he and his wife attended the party Nov. 6 with a dozen friends at the pricy French Laundry restaurant in wine country north of San Francisco.

Newsom said he realized as soon as he sat down at the outdoor table that the group was larger than he had expected to celebrate the 50th birthday of Jason Kinney, a political adviser that Newsom said he has known for 20 years.

“I made a bad mistake,” Newsom said. “I should have stood up and … drove back to my house.

“The spirit of what I’m preaching all the time was contradicted,” he added. “I need to preach and practice, not just preach.”

The lapse came just as California is seeing a surge in coronavirus infections and hospitalizations, and as health officials lobby residents to skip traditional Thanksgiving and holiday gatherings or self-quarantine if they travel.

State and local officials have largely blamed recent increases on such social gatherings, and media experts said Newsom’s failure to abide by his own rules may have hurt his credibility just as the state is trying once again to tighten them. Newsom announced Monday that more counties will move more quickly into increased business restrictions as the state tries to head off a further spike in cases.