Hundreds of social-media accounts with bot-like traits promoted misinformation and content aimed at inflaming racial divisions during both nights of Democratic presidential debates, continuing similar activity during the first set of debates in June, according to data analyzed by The Wall Street Journal.

The bot-like activity on Tuesday and Wednesday nights was consistent with online discussions around Sen. Kamala Harris’s ethnicity during the first Democratic debate, indicating both Ms. Harris, who is black, and racial issues...