Nowadays, the “smoke-filled room” is mostly just a metaphor—but there was a real room that started it all. Well, sort of. The compelling image of the smoke-filled room, a “place of political intrigue and chicanery, where candidates were selected by party bosses in cigar-chewing session,” per William Safire, arose during the 1920 Republican convention. That year, Sen. Warren G. Harding of Ohio was the come-from-behind nominee for president, selected after ten ballots. According to historian David Pietrusza, author of 1920: The Year of the Six Presidents, the room in question is often credited with the phrase “because the people who...