Tom Steyer, a 68-year-old former hedge fund manager turned climate activist, turned exactly zero heads last week when he kicked off his campaign for California governor. Tom who?

To the extent voters have heard of the San Francisco billionaire, it's likely thanks to his batty climate-focused campaign for the Democratic presidential nomination in 2020—in which he spent $4,600 for every vote he received. If anyone is cheering Mr. Steyer's entry into the race, it's local broadcasters hoping he will dump another yacht-load of money promoting himself.