To reenact something is to authorize it again, or to act something out, like a war. Sometimes grown people dress as Confederate or Union soldiers to reenact the American Civil War. Big bushy 1860s beards and all.
Legislators might work to reenact a law that has expired. You can also reenact something by performing or acting it out, the way you'd reenact the battle of Yorktown with your friends playing the roles of British and Continental Army soldiers. People who are involved in historical reenactment reenact such battles with great enthusiasm and authentic costumes and props. The legal meaning came first, from the "decree, sanction, or establish" meaning of enact and the "again" prefix, re-.