Did Mike Huckabee drop out of the fight for the nomination because he lost? Or did he not enter that fight, because he chose not to?
Why does it matter? Well, for academic research, it matters because if we want to discover how the process works and what causes some candidates to win and others to lose, then it's quite important to correctly assess which candidates ran. For the press, it's important because there's at least a case to be made that reporters should concentrate on covering real candidates, not just speculating about those who aren't in. And I suppose it's important for future candidates for the same reason it's important for academics; they, too, want to know what it takes to win, and that involves knowing how candidates lose.
The problem is that we really don't know, and even worse, it's possible that we can't know. It's possible that Huck himself doesn't know. That's the nature of the current nomination process, in which many important events happen well before formal declarations of candidacy. Huckabee had to choose between running for president and continuing his lucrative TV career, but it seems likely that his assessment of the odds of a presidential run succeeding was part of that decision. If Barack Obama had been at 35% approval rather than around 50%; if various GOP bigshots were clamoring for a Huck run instead of a Daniels or a Christie campaign; if whatever efforts he did make went better than they did....well, maybe he's in today, instead of out. One of the variables here is probably how much the potential candidate wants it, but it's probably better to think of that as a factor, rather than the whole story. That is, if Huck wanted it more maybe he's in -- but also, if he wanted it at his current level but his proto-campaign was going better, maybe he's in.
The thing to remember is that the nomination battle generally lasts for three years or so, and that formal declarations of candidates happen very late in the process thanks to a variety of laws and customs, most notably campaign finance laws. That's why Conor Friedersdorf's complaint that the press shouldn't cover undeclared candidates is really wrong. He's right that some press "in or out" speculation is pretty mindless, but restricting coverage to declared candidates would mean missing big portions of the contest. In fact, in many cycles, including both the Democrats and the Republicans in 2000, almost all of the important stuff happened very early, certainly before the voters got involved beginning in Iowa, and probably before anyone declared their candidacy.
So, Huck? Well, he didn't do much to run for the 2012 nomination, but he did do some things. I think the case that he was in at any point is less clear than it was for, say, Haley Barbour...whether he was winnowed out, perhaps, is more about how one looks at things than an objective, clear, fact. That's a mess for research, and a mess for reporters, but if it's the truth then it's probably better to work with the truth than to ignore it on the grounds of analytic simplicity, no?