We’re not entirely sure what sort of marketing push Penguin Press is doing here, having Sesame Street’s Elmo and Disney’s Pluto peruse an advance copy of “Double Down,” the 2012 campaign retrospective written by Mark Halperin and John Heilemann. Maybe like the rest of us, Elmo is trying to figure out how co-star Big Bird managed to become a centerpiece of a campaign that also revolved around bayonets and binders.