RICHMOND, England — Rishi Sunak has a habit of making history. He’s United Kingdom’s first British-Indian prime minister, its first Hindu leader, and at 42 he was the youngest to take the job in over 200 years. He’s also probably the richest person to govern from No. 10 Downing St.

Now 44, Sunak is about to mark new and less flattering records at the U.K. general election on Thursday. After a campaign beset by scandals, PR failures and alleged insider betting, he may very well lead…