MASON CITY, Iowa (AP) — Bernie Sanders' stump speech offers "radical" ideas and a voice rising in outrage as he describes the plight of a disappearing middle class, retirees scraping by on meager Social Security payments and recent college graduates struggling with debt. Sanders is also more willing to jab in Clinton's direction, even while professing to be running a positive campaign. When MSNBC's Andrea Mitchell asked him about releasing a doctor's letter attesting to his "overall very good health," Sanders clenched his fists and broke into a mock shadow boxing session. Part of his appeal has been cultivated by comedian Larry David's portrayal of Sanders on "Saturday Night Live" as a blunt, cranky politician screaming of revolution.