CNN

(CNN) - From the first moments of the debate, the crowd at the Mahaffey Theater played a major role in setting the dynamic for the candidates.

Quick to applaud and to boo, the packed house had all eight GOP presidential hopefuls working to get their applause - and to avoid the jeers.

A testy back-and-forth between former New York Mayor Rudy Giuliani and former Massachusetts Gov. Mitt Romney over immigration early in the debate was punctuated by frequent applause and some jeers.

When moderator Anderson Cooper tried to move on to the next question and Giuliani jumped back to respond to Romney's remarks, members of the crowd booed. Giuliani quickly paused, and the next YouTube question was played.

– CNN's Josh Levs