Picking a nonpolitical “caretaker” as interim mayor of San Francisco until the June election may sound like a good idea, but it’s not.

Let me say up front that I hope the Board of Supervisors picks acting Mayor London Breed as interim mayor. I will support her if she chooses to run for mayor in June as well.

But whomever the board selects to sit in Room 200 until the voters have their say, it should be someone who wants to stay there — be it Breed, Mark Leno, Jane Kim, Angela Alioto or anyone else who declares by the Jan. 9 filing deadline.

Here’s why.

Being mayor of San Francisco requires more than just the ability to put together a $9 billion budget. There are commission appointments to be made. People to be hired. People to be fired. Green lights to be given. Favors to be asked.

That requires a strong leader. Who’s going to take a call in Washington or Sacramento from a caretaker? Which city department heads are going to make controversial decisions with only a bureaucrat mayor standing behind them?

San Francisco’s government would all but grind to a halt. You can’t have that for months on end, just to avoid giving someone a leg up in the June 5 election.

Like it or not, the job of mayor requires power. And you have no power if everyone knows you’re a short-timer.

Oh, the idea sells well. After all, that’s how Ed Lee was named interim mayor in 2011 — by saying he would be a caretaker who would not run for a full term.

But the truth is, if Ed had kept his promise not to run, the Board of Supervisors would have called all the shots for nearly a year. That is, if it could ever have gotten six votes together.

By running for mayor, Ed instantly became a power to be reckoned with.

The move upset a lot of people, especially the other mayoral candidates who spent the entire campaign attacking him as the product of a Willie Brown-Rose Pak power play.

But come the election, the people voted overwhelmingly to keep him on the job, because he was doing a good job. If Ed had flopped as mayor, he would have lost, no matter who was behind him or or how much money was spent on his behalf.

So yes, if the person whom the supervisors name as interim mayor performs well, he or she will indeed have a leg up on the other candidates running in June.

But a lot of things could go wrong as well in the next six months. Homelessness, traffic gridlock, rising rents and car break-ins show little sign of letting up. Being the sitting mayor could just as easily turn into a liability.

Either way, the supervisors’ job now is to make a call on who has the political chops to run the city for the first half of 2018. Their task is not to pick someone who can count the beans and make the June candidates happy.

City’s loss: There is genuine sadness on the streets over the death of Mayor Ed Lee, the likes of which I have never seen. I hear it in the coffee shops, the bars and restaurants and on the sidewalks.

When Mayor George Moscone and Supervisor Harvey Milk were killed in 1978, there was a feeling of shock and anger. Lee’s passing did not trigger any anger. It was just a reminder how quickly something like a heart attack can fell someone still in their prime.

Everyone on all sides of the political spectrum has something nice to say about the guy. Everyone, that is, except the taxi drivers. They still blame Ed for the flood of Uber and Lyft cars that are killing their livelihoods.

Movie time: “Lady Bird.” A great movie. It’s going to be right up there with “Three Billboards Outside Ebbing, Missouri” come Oscar time.

Saoirse Ronan delivers a stellar performance as an outspoken high school student eager to leave Sacramento behind. Total entertainment and a thinking movie as well.

I can’t say the same for “The Shape of Water,” the worst movie I’ve seen all year. The story of a mute cleaning woman in a top-secret laboratory and a guy who looks like the “Creature From the Black Lagoon” left me cold.

I guess I should say it would have been the worst movie I’ve seen all year if I’d sat through the whole thing. I wound up walking out midway through.

And of course there is the big movie of the year, “Star Wars: The Last Jedi.” It really is a big-screen show in the tradition of “The Searchers” and “Lawrence of Arabia.” Totally worth your time.

But heads up: I went to an 8:30 a.m. showing, and the theater was packed.

Want to sound off? Email: wbrown@sfchronicle.com