Mr. Christie will face plenty of competition for relatively moderate and independent voters in New Hampshire. Mr. Bush, John Kasich, Lindsey Graham and Rand Paul all have claims to the moderate and independent vote. Mr. Rubio’s appeal could be broad enough to appeal to these voters as well, even if he is unlikely to advance a message targeted at them. But Mr. Christie’s strength as a campaigner makes it all the easier to envision how he could secure a meaningful foothold in the nation’s first primary. There is a reason, after all, that he twice won the governorship of a solidly Democratic state and was once considered a front-runner for the nomination.

If Mr. Christie’s campaign took off, it would mainly be at Mr. Bush’s expense. It is hard to see Mr. Bush winning Iowa, where the most conservative voters reign, which makes it all but necessary for him to win New Hampshire. A weaker Mr. Bush would give Mr. Rubio a better chance to win New Hampshire, which might be as important to his chances as it is to those of Mr. Bush. It would also give Mr. Walker a better chance of following a win in Iowa with a win of his own in New Hampshire.

But in all those situations, Mr. Christie probably goes back to New Jersey.