President Trump dismissed the youngest candidate in the Democratic field by comparing him to a caricature created decades before Pete Buttigieg was even born. “Alfred E. Neuman cannot become president of the United States,” Trump said when asked by Politico what he thought of Buttigieg, the 37-year-old mayor of South Bend, Ind. The reference to the gaptoothed, big-eared boy made famous as a mascot for Mad magazine did just as much to show Trump’s age as Buttigieg’s. The magazine used the illustration on its cover back in 1956 as a write-in candidate for president. While fairly ubiquitous in pop culture,...