Wherever Newt Gingrich goes these days – stumping in Florida, arguing on televised debates with fellow Republican presidential hopefuls, jotting down notes for his umpteenth book – he carries with him a scary but useful ghost: Saul Alinsky.

The radical community organizer (gone now these 40 years) is the specter on which Barack Obama has modeled his life, Mr. Gingrich warns. It’s no coincidence, he says, that both Alinsky and Mr. Obama were from Chicago or that the president passed up far more lucrative possibilities to become … a community organizer....

Born in Chicago in 1909 to Russian immigrant parents, Alinsky worked his way through the University of Chicago, then dropped out of grad school to organize the poor in the city’s slums, demanding better working and living conditions. He went on to do the same thing in other US cities.

Published the year before he died in 1972, Alinsky’s “Rules for Radicals: A Pragmatic Primer for Realistic Radicals” has been compared with the writing of Thomas Paine, and it inspired many young idealists (including, apparently, Hillary Rodham Clinton, who wrote her Wellesley College senior thesis on Alinsky)....