Be it his self-regard, his disdain for fellow Democrats or his imperious demeanor, Mr. Cuomo alienated allies and enemies alike on his way up in politics, and now finds himself sliding from hero-level worship to pariah-like status with the kind of astonishing speed that only the friendless suffer. It is a downfall foretold in a decade-long reign of ruthlessness and governance by brute force, according to interviews with more than two dozen lawmakers, elected officials, current and past Cuomo administration officials, political activists and strategists in the state.