Eric Garcetti's defection was a blow to Lacey after other high-profile Democratic politicians had withdrawn support or switched allegiances in the high-stakes campaign that has been reshaped after a summer of protests over police brutality.
The loss of support adds to a very unusual dynamic where Lacey, the first woman and Black person to run the nation's largest local prosecutor's office, faces some of her harshest criticism from Black Lives Matter supporters because of her failure to prosecute police officers for fatal shootings. Meanwhile, her opponent, a former police chief, is vilified by police unions and public safety groups because he backs aggressive criminal justice reform. He favors mental health and drug treatment over incarceration.
The contest to run an office with nearly 1,000 lawyers and a jurisdiction that covers the nation's second-largest city and 10 million residents in the country's most populous county is seen as the crown jewel for progressives trying to reshape the way crime is prosecuted at the local level.
Their target is Lacey, the two-term incumbent, and their candidate is former San Francisco District Attorney George Gascon, who was a police officer and chief in two cities before becoming a prosecutor.
More than $12 million in donations have poured into the race. A little more than half is for Gascon, the vast majority from a handful of well-heeled backers supporting justice reforms.
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Among Gascon's backers are billionaire George Soros, who has given $1.5 million, philanthropist Patty Quillin who gave $1.25 million and her husband, Netflix CEO Reed Hastings, who donated $500,000. Most of Lacey's money has come from police unions and other public safety groups.
Gascon has gained support from protests over the death of George Floyd at the knee of a white Minneapolis police officer. That event focused attention on Lacey's record of prosecuting only one LA County law enforcement officer in more than 340 fatal police shootings during her eight years in office.
Gascon has been endorsed by Patrisse Cullors, the co-founder of Black Lives Matter, and that organization's LA chapter has held weekly protests outside Lacey's office to call for her ouster.
The contest presents voters with a choice between a law-and-order DA running an institutional campaign and a challenger riding the wave of a movement for transformational justice reform, said Raphael Sonenshein, executive director of the Pat Brown Institute for Public Affairs at California State University, Los Angeles. It's not clear how LA's deep diversity will come into play, he said.
"Because this movement has reshaped policing politics and brought a younger generation in, it has sort of scrambled the eggs of ethnic politics," Sonenshein said. "You might find young African-American women who are very active in the justice movement strongly support Gascon," while older Latino voters who want a tough-on-crime DA might back Lacey even though Gascon is Hispanic.
In his endorsement, Garcetti said Gascon would "help our county shift the burden from the criminal justice system and jails toward diversion, intervention, and re-entry programs that save money and save lives." Garcetti's father, Gil, who was a two-term DA and once Lacey's boss, also backs Gascon, as do Gov. Gavin Newson and California Sen. and vice presidential candidate Kamala Harris.
Lacey said Eric Garcetti texted her after an Oct. 3 debate to say he and Gascon had been friends for nearly 20 years. He said he would have endorsed Gascon from the start but he got in the race after Garcetti had pledged his support to Lacey in the primary.
Lacey, whose supporters include California Sen. Dianne Feinstein and San Francisco's first Black mayor, London Breed, said she wasn't concerned about Garcetti's switcheroo. She said the loss of endorsements by others, including Democratic U.S. Reps. Adam Schiff and Ted Lieu, who withdrew their endorsement but didn't back Gascon, and Assembly Speaker Anthony Rendon, who switched allegiances, were driven by political decisions in the wake of Floyd's death.
"They have guilt over racial injustice and everybody's trying to prove that, you know, that they're not racist," she said. "Unfortunately, that's been translated into who's the more progressive candidate? What's the more progressive stance? You can be in favor of public safety and be against racism and that's who I am."
Gascon said that the number of politicians supporting him shows the dissatisfaction with Lacey.
"She's having a hard time accepting that she's been a failure," he said.
Lacey has emphasized her experience as a prosecutor - she notes Gascon has never tried a case before a judge - and her ability to run the massive office as key reasons for voters to back her. She said Gascon's policies will lead to move crime and criticized the 2014 Proposition 47 ballot measure he coauthored that reduced some nonviolent felonies to misdemeanors.
A ballot question before California voters this fall would restore some of those penalties.
Gascon, who spent most of his career at the Los Angeles Police Department and then became chief in Mesa, Arizona, and San Francisco before becoming DA there, has said Lacey hasn't held police accountable because she is beholden to them for their financial support, a claim she denies.
He has pledged to reopen investigations of at least four killings by police officers that Lacey decided not to prosecute and has highlighted other cases that raise questions over the use of force.
Lacey said Gascon is pandering to supporters and that when he was San Francisco DA he never prosecuted a police killing case. Gascon said those killings by officers all involved armed suspects. He said he would build on reforms to reduce mass incarceration, not seek the death penalty and that he said would also reduce crime.