Does the weakness of the Republican presidential field have anything to do with Obama's strength as an opposing candidate? Were younger guys who would've been stronger candidates than Romney or Santorum like Jindal, Ryan, Christie, and Thune actually whittled by party actors, or does their decision not to run have to do with them wanting to pick their spot better and wait until the Democrats run a weaker candidate?
My basic feeling is that the apparent weakness of the GOP field is mainly a function of two things. One is that there were no real heavyweights available this time -- unlike, say, the 2008 Democrats, who had two former nominees (one of whom was a former VP), a seemingly successful recent VP nominee, and a former First Lady who was a twice-elected Senator from NY. Republicans had, at best, a very flawed recent VP nominee and...I don't know; Dan Quayle? Beyond that, however, the GOP field, in my view, was OK on paper, with Romney, Perry, Pawlenty, and Barbour making up a reasonably decent group of candidates. Then there are those who sort of ran: Palin, Thune, and perhaps Daniels and others. All of those sort-of candidates got squeezed out by some combination of lack of party support, lack of sufficient ambition, or strategic choices...but in each case, presumably more party support would have tilted the sort-ofs towards full runs.
Anyway, because of the very early winnowing, the eventual field looked much weaker than it really was.Of course, the other big factor was that one of most impressive candidates on paper, the multiterm governor of Texas, ran such a terrible campaign that he now appears to have been more dwarf than serious candidate, but that's probably not really true.