We talk with Jared Cohen, the author of "Accidental Presidents: Eight Men Who Changed America." From the unready to the unexpectedly capable, we discuss the impact of vice presidents who have, on the death of a president, filled the highest office. The framers of the constitution left the question of succession largely unanswered, and the vice president was often chosen out of political necessity or to court a constituency. "Accidental Presidents" suggests it's time we pay more attention to this