Answer: popular sovereignty
Explanation:
Popular Sovereignty is a principle in the United States Constitution that espouses that the Government governs over the people by the will and consent of the people. The people do this by electing representatives to power who will push forward their beliefs.
The general trend of the graph shows an increase in the people voting for president and this shows popular sovereignty because the president is being elected by the will of the people and therefore derives his/her powers from the people.