zerlina, we have yet to hear from former vice president joe biden in terms of whether or not he is going to run. but he does lead in all sorts of polling of likely voters. elizabeth warren has lagged somewhat in those same polls despite everybody hearing from her, knowing since new year's eve that she was doing this exploratory committee. she's been to iowa and the like. who do you see as being the greatest challenge of those not only declared but those ho may declare in a real serious way. >> i think that the biggest challenger right now for joe bide is senator kamala harris. i say that because of the way the calendar is set up. you have the senator from california which is now a super tuesday state who has a real advantage in a state like south carolina where black voters are incredibly important. you can see a scenario in which the delegate math puts her ahead if she's able to take california, which has a lot of delegates as you know, alex.