. >>> and sweet honey in the rock performs live in nerdland. but first, policing progressive politics. ♪ >>> good morning. i'm melissa harris-perry. and that music makes it sound like we're running for president! thursday night in their first one-on-one debate of the 2016, bernie sanders -- campaign, bernie sanders and hillary clinton exchanged jabs over foreign policy. health care and campaign tactics. but the biggest fireworks were sparked by one word. an ideology that has become the focal point of the race for the democratic nomination. progressivism. >> i have a progressive who gets things done. and the root of that word, progressive, is progress. >> all i've said, there is nothing wrong with being a moderate. but you can't be a moderate, you can't be a progressive. >> in your definition, as you being the self-proclaimed gate-keeper for progressivism, i don't know anyone else who fits that definition. >> establish a list of what it means to be a progressive that is unrealistic. >> not at all. >> but the candidates' fight over the meaning of