 He has to be willing to go peacefully and willingly. It's up to Democratic leaders who don't think he can win to persuade him. That remains to be seen. If that were to happen, I actually think the frontrunners would be Hillary Clinton, for example, Kamala Harris, the sitting vice president, who normally would be next in line having been on the ticket, and, of course, the wild card, Michelle Obama, without any question, the most popular Democrat in the country.