got to go. let's talk about joe biden. he took a lot of shots at donald trump. what did he say? >> reporter: he sure did. it's one of the core arguments that joe biden has been making, that he's the strongest democrat to take on donald trump. of course that's open to interpretation and questions. but he went directly after donald trump and said trump has been going after him because he believes he's the strongest democrat in the race. let's listen. >> number one is that vladimir putin doesn't want me to be president. and number two, donald trump doesn't want me to be the nomin nominee. he spent a lot of money to make sure i'm not. i'm flattered. i'm flattered. folks, look, we have got to -- we have got to beat this man.