primary challenge for the sport of it. question, who could be the most effective primary challenger to a trump? rich, start with you. this is "national review" may cover a lot of this. >> it's hard to see how this would work unless trump totally craters. otherwise, you'll get some sort of symbolic challenge from someone like john kasich, 25%, 30%. this juncture, he wouldn't even win ohio. >> what about a ben sasse? mitt romney? >> the two names that come up. mitt romney, the better chance. done it before. more name recognition but a tough poll. >> somebody's going to do it just for the coverage. >> jeff flake ro be interesting. >> president trump runs, he will be the nominee. the question, if he doesn't, it's pence versus the field. >> free for all. when we come back, oh, how the political world has changed in just one year. wish your skin could bounce