>> reporter: tonight, cnn orc polls in nevada and south carolina show hillary clinton with sizeable leads over senator bernie sanders, a big difference from new hampshire where he has led since this summer. high stakes as they prepare to take the stage for the very first democratic debate of this campaign. high stakes but today senator sanders suggested keeping the dialogue on a higher plain. >> let's treat each other civilly and respectfully and let's not try to democrnize people. >> reporter: the 74-year-old self-proclaimed democratic socialist has gone out of his way to be the contrast front-runner. in other words, vote for me, not her. >> i know what i stand for. hillary clinton knows what she stands for. let's have that debate. >> reporter: sanders has yet to do a mock debate. but today for the first time he