Manchester, N.H.

Twenty years ago, a high school senior from South Bend, Ind., won the John F. Kennedy Profile in Courage Essay Contest. Peter Buttigieg’s 2000 treatise for the JFK Library was a paean to—ironically as it would turn out—Bernie Sanders. The 18-year-old essayist praised then-Rep. Sanders for two reasons: He was a man of conviction and candor, willing to take tough positions and adopt the unpopular label of “socialist.” He was also “a powerful force for conciliation and bi-partisanship on Capitol Hill.” “Sanders’...