SACRAMENTO—Leading handily in public polls, Attorney General Kamala Harris appears well on her way to winning a U.S. Senate seat in Tuesday’s election. That probability has led to rampant speculation about who Gov. Jerry Brown will choose to serve the two remaining years in her term.

Conventional wisdom, and the metaphorical betting line around Sacramento, is that Brown, a former attorney general and the son of an attorney general, will not choose a placeholder but instead pick someone who wants to run for the office in 2018, giving him the chance to aid a favored candidate by giving them a two-year head start as AG.