Another of his tweets read: "The handover of the national flag for the change of guard from the president to the president-elect symbolizes the transfer of command."

Calderon is headed next to Harvard University's John F. Kennedy School of Government in Cambridge, Massachusetts. The school announced this week that Calderon will spend the next year as a global public leaders fellow at the school.

Pena Nieto tweeted: "Starting today, I begin to occupy the post of Constitutional President of the United Mexican States. I am confident in my team and I recognize their track record, which supports its commitment to Mexico."