I saw this post the other day on the RCP website, by David Paul Kuhn, and thought I'd offer a brief response.  In the post, Kuhn ponders why, with a the field of so many potential GOP 2012 Presidential candidates, none seem too eager to be the first to declare candidacy.  Here are a few reasons I've come up with, not particularly in order of importance.

1.  They're not that serious.  Every election cycle we see candidates like this.  They're either running to make a point, or running to see to that one of the leading candidates doesn't win, or other people want them to run, but the candidate himself really isn't too hot about the idea of being President- whatever the reason may be, the candidate really doesn't want the job and the responsibilities and stress that go with it. 

A perfect example of this is Fred Thompson.  A great actor who also served a term in the United States Senate, Thompson had a good platform, and a strong following, and at this point in 2007, was considered a frontrunner for the GOP 2008 nomination along with John McCain, Mitt Romney, and Rudy Giuliani.  Ultimately, Thompson's dry wit, at some point, would likely have precluded him from winning, but he easily could've been a VP.  He didn't declare until late 2007, effectively ending any chance he may have had.  I can't speak for why Thompson waited so long.  My guess, based on his behavior, is that, while everyone else wanted him to run, Thompson just wasn't so hot about the idea.  Instead of saying, "Thanks, but no thanks," or giving a Sherman speech, Thompson effectively declined by simply not doing what was required of a seriuos candidate. 

I'm not saying they won't run, but I don't see Chris Christie holding fundraisers, or spending time in Iowa, or making inroads with Republican governors in key states like Ohio and Wisconsin, and Florida (not to mention Virginia).  Barack Obama was able to win the nomination by making connections with people like Ted Strickland, Kathleen Sebelius, Claire McCaskill, Evan Bayh, and Tim Kaine.  He was then able to parlay the coalitions he built in those states into considerable voting blocks, for the general election.  In essence, he won by putting all of the swing states into play and then by forcing McCain have to nearly run the table in order to win.  Not saying he isn't running, but I don't see Christie doing this, and I don't see him winning without doing it, especially considering each party has a different primary nominating system, and the GOP's is even more heavily contingent on the constituency a candidate builds up in a particular state.  Mitch Daniels and John Thune fall into this group, as well- they may be great candidates, but they're relatively unknown.  By the way, if he doesn't hurry up and start getting money, you could probably toss Mike Huckabee into this category, as well.

2.  They're not that good.  George Allen, Howard Dean, Bobby Jindal- these are all people who at one point, had their names floated around as possible candidates for President.  Each had one bad moment, and was instantly disqualified.  Jindal's rebuttal to Obama's 2009 address to congress was widely considered awful; Allen will never live down calling someone "Macaca"; and Howard Dean will forever regret his "I Have a Scream" speech. 

Potential candidates in the 2012 election are no different.  Mike Huckabee was exposed badly by Jon Stewart, on the issue of gay marriage, in a 2008 appearance on the Daily Show.  It's not that gay marriage is all that popular.  Most Americans don't favor it, but the fact that Huckabee couldn't defend his position on it- in front of a comedian- does not bode well for him.  Sarah Palin has, time and time again put her foot in her mouth. 

3.  Obama is very good.  Rank and file Rebpulicans have a difficult time admitting this, but fact are facts, and even if Obama the President isn't very good (and I'm inclined to disagree with this position) Obama the Candidate is masterful.  He just doesn't make many big gaffes.  He just doesn't give many speeches that fall flat.  He's difficult to beat in a debate.  Even in a bad economy and during a nasty battle over the Health Care Bill, his approval ratings were in the mid 40s.  Even people who disapprove like him.  His personal approval is in the 60s.  He beats every GOP candidate in a head to head poll.  This isn't to say he'll be re-elected.  But GOP candidates are not rank and filers.  They're seasoned political veterans.  They know that even an unpopular Obama will be difficult to beat- and one that's as popular as he is now (not that he's really all that popular) will be next to impossible to beat.