Rising homelessness in California has spurred a rodent boom and resurgence of medieval disease. So naturally Democrats in the state Legislature want to ban rat poison.

Earlier this year a rat infestation in downtown Los Angeles near a homeless encampment led to an outbreak of typhus. CatsUSA Pest Control, which was hired to investigate, warned that “poor sanitary conditions” including human waste and hypodermic needles created a “harborage for rodents.” In Los Angeles County cases of flea-borne typhus more than doubled since...