Very soon, the barriers to entry will rise sharply. While I haven’t reviewed the laws and how they interact with a still-in-flux calendar, at some point in the late summer, the difficulties with ballot access will become a barrier for other candidates to enter. If, for example, Christie were to enter late enough in the process that he couldn’t get on the ballot in New York, it would be hard to see how he would put together a campaign unless everyone else rolled over for him.