The Republican 2012 presidential field is, perhaps, more well known for who's declined to run as it is for its actual candidates. One by one, potential contenders have either decided against a run or declined fervent pleas to take on President Obama: Donald Trump, Govs. Mitch Daniels (Ind.), Haley Barbour (Miss.), and Chris Christie (N.J.); former Govs. Mike Huckabee (Ark.) and Jeb Bush (Fla.); Sens. John Thune (S.D.), and Marco Rubio (Fla.); and Rep. Mike Pence (Ind.), to name a few. Why are so many Republicans sitting 2012 out? Here, five theories:

1. Nobody thinks they can beat Obama
Each Republican who has bowed out has his reason, be it "personal, strategic, financial," says Roger Simon at Politico. But many also have a bigger reason: "They doubt any Republican can beat Obama in 2012, and they would rather wait for an open seat in 2016." They are wrong that Obama is unbeatable, but he's not going to just hand them the keys to the White House, either.

2. They're afraid of the negative ads
There are about a billion reasons "the 2012 race is characterized more by those refusing to run than by those running," says John Podhoretz at Commentary. Obama is aiming to raise $1 billion, and he'll use it to accomplish one goal: "Destroy the eventual Republican nominee." Everybody already has an opinion of Obama, but imagine being the GOP nominee trying to introduce yourself to the country while Obama is spending hundreds of millions making sure that first impression is "unabashedly hostile." It's too "horrible to contemplate."

3. The media will shill for Obama
"I don’t expect Obama to sling mud; it isn't his style," says Bill O'Reilly in the Boston Herald. But his blogger fans and the liberal media "will be ready, willing and able to do the dirty work." It's not so much that the "elite media" favor Obama, but they share his liberal ideology, and the end result is the same: "If you thought the established press promoted Obama the first time around, wait until you see what lies ahead." The Republicans who have opted out are "smart guys."

4. There's no need for more candidates
"Republican elites" are in full-on panic mode "over the apparent weakness of their presidential field," says Jamelle Bouie at The American Prospect. But they needn't be. The woeful stories about the 2012 GOP field look eerily similar to the 1991-92 stories about the Democrats. And of course, "then-obscure Gov. Bill Clinton of Arkansas" came out of nowhere to topple the first President Bush — who was widely viewed as unbeatable after the Gulf War, until the economy tanked. "If history is any guide, there's simply nothing about this particular crop of Republican candidates that dooms them in 2012, given a poor economy."

5. Only chumps run for president
Why in the world would "any sane person run for president" these days? asks Doug Mataconis at Outside the Beltway. A century ago, presidential candidates barely campaigned — it was considered "unseemly" to sell yourself that way. But these days, you give up a year and a half of your life, or "longer if you happen to be 'lucky enough' to win," to work 24/7 for no pay and little chance of a payoff at the end, and your every word is parsed. No wonder no one wants the job.