A key backer of San Francisco granting noncitizens the right to cast ballots in school elections now wants the city to spend as much as $500,000 a year to warn undocumented residents that registering to vote could point the feds their way.

Supervisor Sandra Lee Fewer was on the school board when she urged voters to pass Proposition N in November 2016, arguing that it would give immigrants more of a say in their children’s education. Its passage made San Francisco the first California city to give noncitizens the right to vote in any election.

Of course, something else happened in that election — Donald Trump won the presidency. His anti-immigration policies are at the heart of Fewer’s switcheroo.

“Those who choose to vote should know some of the risks involved,” Fewer said.

The first election in which noncitizens will be able to vote is in November. City elections Director John Arntz says his office is looking at creating a form for noncitizens that would require them to give their address before they could cast a school-board ballot.

Fewer worries that the feds could subpoena voter registration rolls, looking for undocumented immigrants, and “we would have to turn them over” — addresses and all.

An estimated 44,000 undocumented immigrants are living in the city. Even though Prop. N applies only to noncitizens who are parents or guardians of children in public schools, that’s still a lot of people to warn that immigration agents might come calling if they sign up.

Under guidelines being drawn up by the Board of Supervisors, warning notices to prospective noncitizen voters would have to be translated into as many as 48 languages and circulated not just to schools, but also preschools and community resource centers. The warnings would alert those thinking of signing up that the feds may have access to their personal information.

Fewer estimates that the city may need as much as $500,000 a year to keep everyone informed on the issue. That money covers everything from administrative costs and materials to grants for nonprofits to hire outreach workers. But even her call for an initial $125,000 to get the ball rolling drew a less-than-enthusiastic response from Mayor Mark Farrell.

“If the Board of Supervisors believes another outreach program is needed, they should work with the Department of Elections,” he said.

Farrell was the lone supervisor to oppose putting Prop. N on the ballot in 2016, calling it a “slippery slope.”

By the way, we asked Immigration and Customs Enforcement whether it would really go after noncitizen voters, looking for undocumented immigrants. The agency sent us to the U.S. attorney’s office in San Francisco, where spokesman Abraham Simmons said, “No comment.”

Judicial mess: The whip is coming down on Contra Costa County prosecutors who don’t clean up after lunching grand juries.

The message: Get out the dish rag, or someone else is going to be pitching indictments to the panels.

“Not only is this a responsibility, it is a matter of common courtesy,” Senior Deputy District Attorney Mary Knox wrote in a recent memo to the staff.

At issue: the community room where prosecutors make their arguments for indictments to 19-member criminal grand juries. The meetings can last for hours, so jurors often bring their lunches or use the room’s small kitchen area.

But they haven’t been cleaning up after themselves, so a staffer has been doing the job and hauling out the “stinking trash,” Knox wrote.

“This is not acceptable and will not continue,” she said.

Knox said she sent out what she called the “mean mommy” memo because the room, which other groups also use for meetings, was becoming an embarrassment.

“Since the cutbacks of the 2007 recession, we have only one janitor working two half-days a week to clean an entire four-story building” in downtown Martinez, she told us. “The janitors don’t even clean the offices — we have to do that.”

So prosecutors can ask grand jurors to pick up after themselves, Knox wrote, or the lawyers can do it. But if nothing happens, she’ll find other prosecutors to lead the cleanups — and make the cases.