1. The candidate’s opponent challenged her to debate the issues. The opponent had thrown down the gauntlet and she was ready to pick it up and accept the challenge.
2. If you don’t want to start a fight with Carl, don’t throw down the gauntlet

A gauntlet is a glove from a suit of armor. The expression originates from a medieval custom of throwing down one’s gauntlet as a way of challenging an enemy to a fight. One accepted the challenge by picking up the gauntlet.