SACRAMENTO, Calif. — California Gov. Gavin Newsom has had a summer of muddled messaging and bad news in the coronavirus fight, a trend crystallized this week by his delayed response to a data error that caused a backlog of nearly 300,000 virus test results.

"The buck stops with me, I'm accountable," he said in a tense Monday news conference, his first appearance since state officials revealed the error a week earlier. "No one's trying to hide that, no one's trying to mask that, we're owning that, we're moving forward to address those issues."

His tone couldn't have been more different than it was in March, when California's public battle with the virus began and the state initially avoided the worst outcomes. In commanding news conferences held almost daily, he announced the country's first statewide stay-at-home order and won mostly adherence from the state's 40 million residents.

But things began to change in May, when Newsom, under pressure from business leaders, allowed parts of the economy to begin reopening under a complicated, county-by-county process. Within weeks he reversed course as confirmed cases and the positive test rate rose.

The data backlog, which began at the end of July and continued because of a series of errors, led to the state under-counting the rate of virus spread and halted decision-making about what parts of the economy could open. Newsom has repeatedly stressed that those decisions will be made based on data.

The snafu also poses a political problem for Newsom, a Democratic rising star who is up for reelection in 2022 and is believed to have his eye on even higher office. His decisions in the crisis will help forge his legacy — good or bad — and so far, they are getting mixed reviews.

"The reopening was inconsistent and confusing, the criteria that he had set up in order to enter those different phases he appeared to discard," said Rob Stutzman, a Republican and former communications adviser to then-Gov. Arnold Schwarzenegger who said Newsom started out strong at the beginning.

Dr. Eric Topol, head of the Scripps Research Translational Institute in San Diego, said the data collection problem is related to the state's abrupt reopening. California appeared to be on a "golden path" by shutting down early and leading the way in its effort to contain the virus. Since then, it's been "one mistake after another" when Newsom began allowing things to reopen, Topol said.

The surge of cases meant the state suddenly had more data than it could process, he said, asserting the state was woefully unprepared.

"You would think we could have the best IT for the pandemic. There's just no excuse. And we've had months," he said.

Newsom's announcement last week that things were trending in a positive direction was immediately overshadowed by news of the data errors. The state's top public health official, Dr. Sonia Angell, abruptly resigned, and Newsom declined to get into the details. He later said "decisions were made" to change the team.

The glitch wasn't the first time Newsom and his administration gave unclear or incomplete responses to virus-related issues. Since early summer, schools had sought guidance from the state on when and how they could reopen, and by July many districts were making decisions on their own. Then, Newsom announced schools in most counties couldn't immediately reopen for in-person instruction, sending many parents into panic mode. He later clarified that some elementary schools could apply for waivers, though the process for doing so was far from simple.

Lawmakers from both parties have also criticized him for not acting swiftly enough to fix problems at the state employment department, as some claimants face weeks-long delays to get unemployment checks.

Advocates also say Newsom's administration failed to act quickly enough to protect Latino workers from the virus and its economic harm. Latinos make up nearly 60% of the state's confirmed cases even though they represent 39% of California's population.

Jacqueline Martinez Garcel, chief executive officer of California's Latino Community Foundation, said access to financial help for those who have lost jobs has been difficult.

"Why is it that the fifth-largest economy in the world and the tech hub of the country and the world can't figure out the computer problems that we're having for people to access unemployment?" she said.

Republican Assemblyman Kevin Kiley, a frequent Newsom critic, called for a legislative oversight hearing about the data failures, but Democratic Speaker Anthony Rendon isn't planning one.

"For months Californians have put their lives on hold based on data. Now we've learned the data is wrong, and the Assembly can't be bothered to investigate," Kiley said in a statement.

Others noted the governor is operating in an unprecedented crisis. For most people, the new coronavirus causes mild or moderate symptoms, such as fever and cough that clear up in two to three weeks. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia and death.

Democratic state Sen. Scott Wiener said Newsom and his team "have been drinking water from a fire hose" for months.

"No matter what he does he will be criticized. He'll be criticized for not doing enough to restart the economy or he will be criticized for reopening too quickly leading to more virus spread," Wiener said. "My take is that he has accepted that and that's the price of leadership."