Overview: Monday on the NewsHour, following the latest round of voting, Amy Walter and Tamara Keith talk the changing face of the 2016 race. Also: The proposed Syrian ceasefire takes effect next week, the Supreme Court remembers Antonin Scalia, U.K. considers European Union exit, how elephants could help cure cancer, a son celebrates his father’s activism with poetry and a 106-year-old dances with Obama.