I did a search and the only president to ever do this before being elected was John F. Kennedy.
"Yes, a president-elect has laid a ceremonial wreath at the Tomb of the Unknown Soldier at Arlington National Cemetery before being sworn into office.
President-elect John F. Kennedy participated in this ceremony on January 20, 1961, the morning of his inauguration. The event took place just hours before his swearing-in ceremony as the 35th President of the United States."
I did a search and the only president to ever do this before being elected was John F. Kennedy.
"Yes, a president-elect has laid a ceremonial wreath at the Tomb of the Unknown Soldier at Arlington National Cemetery before being sworn into office.
President-elect John F. Kennedy participated in this ceremony on January 20, 1961, the morning of his inauguration. The event took place just hours before his swearing-in ceremony as the 35th President of the United States."