the public. that might benefit that you win eventually when trump faulters. reporter: a fresh spotlight on ben carson. aides say he won t back away from drawing distinctions with trump. i m not going there. next question. reporter: but will not go after him in a personal way. the debate stage is unforgiving, creating a series of make or break moments for the candidates that can soar i have as much experience in the congress as jack kennedy did when he sought the presidency. you are no jack kennedy. reporter: or flop. a lot of static. i can t. the third one i can t. sorry. reporter: leaving a lasting memory tied to each candidate for better or for worse. 24 million people watched last month s debate. for the candidates, especially the ones that are struggling, this is their best chance to reach out to a larger audience