Jay Cost has a pretty good article out today arguing that the main reason Mitt Romney is doing so well is that he was lucky in one critical way: there just weren't very many potential serious opponents out there, thanks to GOP losses in 2006 and 2008 and some apparently random quirks of fate (such as that the Governor of California wasn't eligible, for example).
I think there's some truth to it, but one has to be careful with this sort of analysis. Cost notes that every GOP nominee since 1948 was either a Senator, a Governor of a decent sized state, or a high-ranking exec branch official. That's true...but it's also perhaps a bit misleading. If we expand to include both parties, we get Bill Clinton from small-state Arkansas. If we also expand to include candidates who came fairly close to winning, we might add Dick Gephardt from the House, and perhaps even Jack Kemp. Cost limits his potential field to Senators who have completed a full term, but of course Barack Obama didn't, and neither had John Edwards in 2004, who was just completing his term. Cost also includes recently retired Governors, but not recently retired Senators.
The thing is that thinking about this stuff is tricky. On the one hand, it's certainly a useful exercise to use the past as a guide to the future: knowing that no one similar to Herman Cain or Michele Bachmann had ever come close to a nomination was a pretty good indication that neither of them would, either. But caution is very much in order: I'm sure that it wouldn't take very long to imagine something that would seem to have disqualified every past nominee on the grounds of no one with that particular trait (or missing that particular trait) had ever won before.
I guess the other thing I'd say is that Cost's pyramid structure makes plenty of sense (with serious candidates at the thin point at the top, and all GOP voters down at the bottom), but he doesn't work it enough. I did a post a ways back in which I talked about various tiers of presidential candidates. The top tier would be former and sitting VPs (or Gore 2000 or Mondale 1984), previous runners-up (Reagan 1980 or Dole 1996). The second tier are the people Cost talks about: big-state current and recent Senators and Governors. And then you would have Senators and Governors from small states, and maybe cabinet officials, prominent Members of the House...you get the idea.
Anyway, the point is that Romney was certainly lucky this time and in 2008 that there weren't any real top tier candidates available (although you can make a case that Dan Quayle was top-tier and could have been a formidable candidate had he attempted to revive his career). And then of the second-tier people...well, it's hard to know. Surely some potentially serious contenders, such as Bill Frist and Jeb Bush, really didn't want to run this time. But others -- Huckabee, Palin, Daniels, Pawlenty, Barbour, Thune -- sure seemed to at least kick the tires a little. As you've heard me say before, we really don't know whether they wound up not running now because they chose not to try or because they did try and were defeated: they were politely told that they would not win the support of party actors whose support is necessary to win. And if they were defeated, we don't know to what extent it was because of some weakness in them as potential candidates, or to what extent it was because they were beaten by Mitt Romney. And without knowing those things, it's hard to know how much of Romney's current position is luck and how much is skill.