Right now? I can't think of anyone, but that's basically what happened with republicans this last election. They didn't have anyone who stood out, so Trump was able to get the nomination. Maybe Bloomberg because of name recognition if he runs on the democrat ticket or possibly @ticket2ride04's most wanted lover, Newsom.
Those two would be a formidable ticket. Plus it offers cover for Gavin if he were to lose. It is hard to unseat a sitting President and losing would harm Gavin. Think about Romeny. He should have waited until Obama was out and he most likely would have won it all.i’ll take both those two right now...my fingers are crossed, at least.