|Mitt Romney and Nancy Pelosi|
Nancy Pelosi is in command of the Democratic Party and its most critical issue. The Party wants a winner, and recognizes its frontrunners are politically flawed. They may beat Trump in hypothetical polling questions, but each raises questions as to their ability to take him on, out-maneuver him in key states and actually lead the country without having a new political pile-up. The Democratic ticket needs balance, and Cory Booker, whose debate performances have had some moments, would add some.
Romney vs. Pelosi is unlikely, but it would be a contest on direction and policy and not an endless vulgar war of name-calling.