Then came June. After George Floyd’s death, protesters gathered outside the police station. Others stormed the beaches. On June 6, a man alleged to be an anti-government extremist ambushed and killed a 38-year-old sheriff’s deputy in Boulder Creek, a mountain town to the north. More than a thousand people stood shoulder-to-shoulder at the deputy’s vigil — many without masks. Officers, spread thin, needed to triage. “We no longer had the bandwidth to go enforce an ordinance down on the beach,” Mr. Escalante said.

Dr. Newel began to think differently about what she was asking the police to enforce. What if an officer asked someone to get off the sand, and that person didn’t comply? She imagined a scenario where that officer might physically drag the person to a police car. “The optics of trying to enforce a beach closure became impossible,” she said.

Further complicating matters, on June 12, Mr. Newsom reopened hotels to tourism without lifting the shelter-in-place order. The following weekend, flouting Dr. Newel’s closure order, some 55,000 people filled the three-quarter-mile stretch of sand on Santa Cruz’s main beaches. At a news conference on June 25, she announced a spike in Covid-19 cases so drastic the county redesigned its online epidemiologic graph. “It has become impossible for law enforcement to continue to enforce that closure,” she said. “People are not willing to be governed anymore.”

The statement reverberated in the blue state. More angry messages ensued, uglier than before. Murderer, one wrote. Our deaths will be on your hands. Another read: If any of my family members or friends die, I’m coming for you.

Dr. Newel is no stranger to crises. She beat cancer in 2010, and lost her eldest son to an opioid overdose in 2016. Weeks ago, her aunt died after catching Covid-19 in an Ohio nursing home. Though she admitted to “feeling weary,” she said, she intends to stick it out. “I feel like I’m the right person in the right place at the right time to do this job,” she said, standing near the Santa Cruz Beach Boardwalk in late July.

Since then, the situation has grown increasingly dire. Santa Cruz County recently recorded more cases in one week than in all of April and May combined. More than 20 outbreaks are being tracked across the county, including outbreaks in four skilled nursing facilities and a homeless shelter. The county expanded the number of agencies empowered to enforce local and state health orders — but not in time to keep Santa Cruz off the governor’s watch list. On July 28, the county’s indoor gyms, hair salons and places of worship were once again forced to close.

This time, though, Dr. Newel didn’t announce the closures with a local health order. She defaulted to the state health department. It wasn’t that she was afraid of the inevitable backlash, she insisted. She just thought that if she issued the order herself, the outcome would be insignificant.