Sen. Dianne Feinstein is wading into the debate over the Washington High School mural, telling the San Francisco school board that covering the Depression-era artwork that includes depictions of slavery and the genocide of Native Americans would be “to deny our past and to fail our students.”

Feinstein said that while she is pleased that the board took “a step back” from its vote to paint over the 1,600-square-foot “Life of Washington” in response to concerns that it offended and disturbed some students, she cannot support covering the mural’s panels, either.

“To cover them in any way prevents them from being used in the manner intended ... as teaching tools,” Feinstein wrote in an Aug. 14 letter to board President Stevon Cook. “It also bears the question of what art or written word will be next?”

Cook did not return requests for comment on the Feinstein letter.

The school board set off a firestorm when it voted unanimously to paint over the mural at an estimated cost of $600,000. Ironically, the work by Russian immigrant Victor Arnautoff was intended to reveal the darker side of the nation’s early days and criticize slavery and the genocide of Native Americans. Still, many found the images hurtful.

Because of the ensuing outcry over the destruction of the mural — and the high cost of painting over it — the board instead opted to place panels over the offensive portions of the mural. That could cost as much as $825,000, according to the district’s estimate.

“That’s all the detail we have to share at this time,” school district spokeswoman Laura Dudnick said of the costs. “We are heading into an (environmental impact report) process which will be public and will provide a lot more detail regarding costs associated with various options.”

Jon Golinger, a spokesman for the Coalition to Protect Public Art, which is considering placing a ballot measure before voters on the issue in March or November 2020, said, “I understand that some of the big donors to the school system are not happy about the cost.”

Local Democratic party officials, meanwhile, fear a ballot measure would be a distraction and force candidates to take sides in what many see as a no-win situation. The hope is that taking the destruction of the murals off the table will calm things down a bit. And that, by the time all the needed reports and studies are done, the elections will be over.

Spot test: With the race to replace San Francisco District Attorney George Gascón heating up, we asked the leading candidates to weigh in on the initial release of Austin James Vincent after he allegedly attacked a woman outside her Embarcadero condo complex while talking about saving her from robots.

We asked what they thought of Judge Christine Van Aken’s decision to free Vincent — against the wishes of the district attorney’s office — and how they would have handled it as the city’s top prosecutor.

Former prosecutor and ex-Police Commission President Suzy Loftus pointed the finger at the D.A.’s office, saying it could have and should have done more.

“They failed here,” Loftus said.

“When a judge is planning to release someone who the line prosecutor thinks poses a public safety risk, we will send a supervising prosecutor to court to review what has been presented and provide additional argument as needed,” Loftus said. “I ordered the transcript of the first hearing, and none of this happened.”

Assistant Alameda County D.A. Nancy Tung said, “From the outset, Mr. Vincent was violent, dangerous and unstable, and should have been kept in custody by Judge Van Aken.”

Tung said she had not seen a transcript of the hearing, “so I don’t know what arguments were made by the prosecutor handling the case.”

“That said, I thought D.A. Gascón undermined his own prosecutors when he sent out a series of tweets arguing that people suffering from mental illness and drug addiction — who, like Mr. Vincent, pose a threat to public safety — should not be detained in jail,” Tung said.

Deputy state Attorney General Leif Dautch said the Vincent case “captures the frustration I hear from people every single day.”

“If city officials have decided that the criminal justice system is not the right place for those with mental illness or drug addiction, then those same city officials need to step up and create a robust system that ensures people actually get the treatment they need,” Dautch said.

“Let’s put aside the novelty ‘first in the nation’ stuff for a minute and address the fact that many people don’t feel safe walking around their neighborhood at night,” he said. “That’s why I have proposed transforming the nearly empty juvenile hall into a mental health justice center to treat people battling mental illness.”

The fourth candidate in the race, Deputy Public Defender Chesa Boudin, who is running on a platform that includes calls for an end to mass incarceration, did not reply to requests for comment.

San Francisco Chronicle columnist Phil Matier appears Sundays and Wednesdays. Matier can be seen on the KPIX-TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call 415-777-8815, or email pmatier@sfchronicle.com. Twitter: @philmatier