Stan Greenberg, polling guru for President Bill Clinton's 1992 campaign, takes some shots at much-criticized pollster Mark Penn in his new book recounting his prominent campaign work -- some of it in conjunction with Penn. Among the juiciest: Greenberg accuses Penn's polling methods of being "rigged." Penn supplanted Greenberg both on Clinton's team and on the British Labour Party's 2005 campaign, and it was the latter experience from which the "rigged" accusation springs. Though rife with sour grapes and potentially motivated by vendetta, Greenberg's accusations echo some made after Penn's unsuccessful stint as top man on Hillary's primary run, according to Mark Blumenthal at Pollster.com. Penn responds that his "surveys for the Labor Party as "extremely accurate," says Greenberg was excluded from information because he was "not in the loop," and describes Greenberg's attacks as inaccurate and "unsubstantiated."