Larry Summers in his West Wing office, two short flights of steps above the Oval Office. Photograph by Steve Pike.

Larry Summers is not an easy man to catch off guard. Behind his rumpled, jowly, professorial façade hides the world’s shiniest gold-plated résumé and one of its fiercest intellects. No less an authority on presidential power than Henry Kissinger once told Tim Geithner, now the Treasury secretary, that Summers should have a permanent job at the White House, solely to sort out for the president—any president—the good ideas on economic policy from the dumb ones.

When Barack Obama was elected, many thought that Summers, who headed Treasury during the final 18 months of the Clinton administration, would find his...