The inauguration of a U.S. president is traditionally a highly scripted celebration, with seating charts, schedules, dress rehearsals and planning committees that map each moment of the history-making day from start to finish.
But sometimes the unexpected happens.
A chief justice stumbles while administering the oath. The bitter cold forces the inaugural ceremony to move inside. A president decides to break from tradition and walk with his inauguration parade down Pennsylvania Avenue to the White House.