this is where it all happens, the venetian las vegas, the site of the last republican primary debate of 2015. it is only here on cnn. it is such an important moment in this campaign. the first debate after the attacks in paris, the first debate since the attacks in san bernardino, and national security will be the focus here on tuesday. as for the debate stage itself in the venetian theater behind me, donald trump will be center stage on the main stage, but this time, ted cruz will be standing right next to him. this is the first time cruz has moved to the center shift based on the polling like this one from the des moines register out this weekend that shows ted cruz moving into first place by a lot, a ten-point lead over donald trump in iowa. nationwide druch is still out