But what will it be worth?

Here is a not-necessarily-complete list of potential 2012 Republican presidential candidates. For the sake of fairness, I've listed them in alphabetical order. But, of course, I've already tipped my hand. When you get to the bottom (but most definitely not the top) of the "P" listings, you'll find my favorite:

• Mississippi Governor Haley Barbour
• Former Florida Governor Jeb Bush
• Former Speaker Newt Gingrich
• Former Arkansas Governor Mike Huckabee
• Louisiana Governor Bobby Jindal
• Alaska Governor Sarah Palin
• Minnesota Governor Tim Pawlenty
• Former Massachusetts Governor Mitt Romney
• South Carolina Governor Mark Sanford
• South Dakota Senator John Thune

Will that nomination be a prize worth having?

Running against an incumbent president is always difficult. The challenger goes around in a rented campaign plane, making promises about the future. The incumbent swoops down in the most impressive aircraft in the history of aviation, and often doles out real right-now money, in the form of federal grants to local projects.

Exactly how difficult has that been? During the past century, 11 presidents survived through a complete first term, and sought reelection. In four of those cases, the challenger unseated the incumbent. Most of the other seven challengers went on to be appointed or elected to public office, but none of them were nominated for national office ever again.

The list of 11 challengers (a list on which the aforementioned prospects want to be the 12th) is as follows:

• 1912 -- Woodrow Wilson -- defeated incumbent William H. Taft, and was president from 1913 to 1921.
• 1916 -- Charles E. Hughes -- was secretary of state (1921-5) and chief justice of the United States (1930-41).
• 1932 -- Franklin Roosevelt -- defeated incumbent Herbert Hoover, and was president from 1933 to 1945.
• 1936 -- Alfred Landon -- never served in public office again.
• 1956 -- Adlai Stevenson -- was ambassador to the U.N. (1961-5).
• 1972 -- George McGovern -- won one more term in the U.S. Senate, where he served until 1981.
• 1980 -- Ronald Reagan -- defeated incumbent Jimmy Carter, and was president from 1981-9.
• 1984 -- Walter Mondale -- was ambassador to Japan (1993-6).
• 1992 -- Bill Clinton -- defeated incumbent George H.W. Bush, and was president from 1993 to 2001.
• 1996 -- Bob Dole -- never served in public office again.
• 2004 -- John Kerry -- remained in the U.S. Senate, where he now chairs the Committee on Foreign Relations.

One scenario that doesn't appear on that list is: 1) candidate loses to incumbent, but 2) gets national exposure, and 3) is rewarded by his party with a chance to run for president four years hence, when there's an open race (except, of course, during the period when FDR was president-for-life). But this is a small sample, so there's no saying that couldn't happen.

It's much too early to predict whether President Obama will be in the Taft/Hoover/Carter/Bush category but, on the basis of those statistics, the odds of his avoiding that fate are in his favor.

Of course, all of those GOP hopefuls want to win. But I wonder if some of them, especially young up-and-comers such as Jindal and Pawlenty, are thinking in terms of positioning themselves for 2016.

Most of the seven also-rans on the list of past candidates, had some significant achievements after their presidential candidacies. But no one runs for president hoping to become an ambassador or a congressional chairman. All of those Republican hopefuls are trying, against the odds, to win the presidency either in 2012 or 2016.