A registered Democrat, Robert Pozen has little to gain politically from the Social Security solvency plan that he drafted and that now is heralded by President Bush, whom the former Massachusetts economic development chief voted against in November. Nonetheless, Pozen has become a favorite witness at congressional hearings, promoting his idea of "progressive indexing" for future benefits. At age 58, Pozen has no personal stake in the current Social Security debate because neither President Bush nor Congress has advocated changing the existing system for workers over 55. It's a fair bet, too, that Pozen, a graduate of Harvard College and...