New Jersey Gov. Chris Christie dropped out of the presidential race today. That's not that surprising, after his sixth-place finish in yesterday's New Hampshire primary. But what is a bit interesting is speculation that his decision might have been prompted by the rules governing who will get to participate in the next Republican debate, which will take place this Saturday, February 13, and will be aired on CBS.

By placing sixth in New Hampshire, Christie did not qualify for the debate. But he would have qualified, and thus possibly stayed in the race, if he had gotten more votes than Marco Rubio. There was a pretty big difference between the two candidates' vote totals (about 9,000 votes). Nonetheless, it is reasonable to consider whether there are 9,000 voters in New Hampshire who did not vote for Christie but would prefer he stay in the race. For example, consider the more than 11,000 people who voted for Carly Fiorina, who also just announced that she is ending her bid.

These multicandidate, multistage electoral contests are classic situations for strategic voting. In particular, until the very last vote the proper way to think about whom you should vote for involves thinking not only about whom you like the most, but also about how your vote will affect the candidacies of the other alternatives. Particularly in this primary season, the "early" states will effectively determine the set of candidates that voters in the later states get to pick from.

Of course, I don't believe that Christie (ever) had a strong chance of winning the nomination. But as we saw in the previous GOP debate, Christie's presence in the race might have affected who will win it.