Illustration: Tim Bouckley They call him an opportunist and a vulture who’s capitalizing on a tragedy to promote his dangerous Medicare for All agenda. Over and over , they invoke his name alongside those of left-wingers the likes of Bernie Sanders. For the target of these attacks, Wendell Potter, it’s a familiar playbook — after all, he helped write it. “I guess I should be flattered,” he jokes. Potter is the nation’s most prominent health-care whistleblower, a former Cigna executive who