Representative Michele Bachmann burst like a nova onto the presidential race thanks to a smooth and confident performance that lit up the stage at a Republican debate in June. Now, with polls showing her popularity dwindling, her campaign is hoping to recapture its early momentum by again showcasing her strengths in a national debate on Monday night. Mrs. Bachmann won the first important test of the Republican race in a straw poll in Iowa last month, but she has been upstaged ever since by the entrance of Gov. Rick Perry of Texas into the race. She was uncharacteristically muted at...