jeff is live in washington for us with more. jeff? >> reporter: good morning, michaela. a new window into vice president joe biden's thinking. he believes he would be the best candidate. he sheds new life on what his son bo told him before he died. >> some people have written that bo, on his death bed said dad, you have to run. nothing like that ever, ever happened. bo, all along thought that i should run and i could win. there was not what is made out as this hollywoodesque thing that at the last minute bo grabbed my hand and said dad, you have to win one. wasn't anything like that. >> with biden on the sidelines, hillary clinton and bernie sanders went head-to-head in iowa. sanders called himself a principaled progressive. he supported gay rights long