Republican front-runners square off at the presidential debate, but it was the underdogs who shined the most. SUBSCRIBE to ABC NEWS: .br Republican front-runners square off at the presidential debate, but it was the underdogs who shined the most. SUBSCRIBE to ABC NEWS: . TIMESTAMPS IN .br Tense moments during debate in Colorado with candidates turning the tables on the moderators.br Make ABC News your daily news outlet for breaking national and world news, broadcast video coverage, and exclusive interviews that will help you stay up to .