It tends less strongly to exclude members of Congress, particularly House members but also senators, whose extensive voting records inevitably contain material that is politically damaging at some point in the process. The process has become so lengthy that candidates often come up with strategies and programs that are rendered obsolete by the time of the next presidential inauguration.
All that said, we are stuck with it -- or stuck with the version of the schedule that the national Democratic and Republican parties, acting for once in concert, and the various state parties and state legislatures can agree on.
So it may be worthwhile, before trying to assess the chances of likely, putative and possible Republican candidates in the 2012 cycle, to dismiss some of the rules of thumb that have arisen over the years.
The first is the notion that Republican nomination always goes to the candidate next in line in seniority.
Yes, Republican primary voters and caucus goers are probably more inclined than Democrats to defer to seniority. But when you look back at the Republican nominating contests in the post-1968 era, and there are not many of them, you find that most of the nominations were close-run things.
Ronald Reagan came within a few convention votes of upsetting incumbent President Ford in 1976 and would probably have won if he had gotten 2,000 more votes in New Hampshire. Reagan's victory in 1980 was contingent on a number of close calls, as readers of Craig Shirley's "Rendezvous with Destiny" know.
The first George Bush's victory in 1988 depended on a big win in the South Carolina primary rescheduled by his campaign manager Lee Atwater, which would probably not have occurred if Atwater's premature death had come a few years earlier. In 1996, 8,000 more votes in New Hampshire would have made Lamar Alexander rather than Bob Dole the chief challenger of Pat Buchanan and hence the party's nominee.
The next-in-line candidates did win in 2000 and 2008. But George W. Bush only narrowly survived a rout in New Hampshire, and John McCain's strategy eight years later -- wait for all the other candidates' strategies to fail -- is one that usually guarantees defeat rather than victory.
As for 2012, the next-in-line candidate is said to be Mitt Romney, on the basis of a successful business career and a single term as governor of Massachusetts.
The next rule that needs to be debunked is that Republican candidates must pass a litmus test on cultural issues, especially abortion. This was true in 1988, 1996 and 2000, when religious conservatives were a newly energized political force and one stirred to action by Bill Clinton's misconduct.
But Sept. 11 changed a lot of things, including this old rule. A pro-choice stand on abortion didn't prevent Rudy Giuliani from leading Republican polls until November 2007, when his appointee as police commissioner, Bernard Kerik, was indicted. And going to all 99 counties swearing he was a right-to-lifer didn't save Mitt Romney in the majority-religious conservative Iowa caucuses in January 2008.
The financial crisis and protracted recession have once again changed the focus of Republican voters. Polls have showed that Tea Party activists, who number in the hundreds of thousands, tend to be cultural conservatives, but they moved into politics to oppose the stimulus package and Obamacare, not abortion and same-sex marriage.
The third rule that may not be applicable this time is that you have to start early to win. Tell that to Bill Clinton, who announced his candidacy in October 1991, just four months before the Iowa caucuses. Many potential and putative Republican candidates this time seem to be biding their time. You may be able to ramp up a campaign pretty quickly in the Facebook era.
The presidential nominating process is a zero-sum game in which all but one of the competitors must lose. In looking over the possible field of candidates, it's not hard to come up with a reason why each of them cannot possibly win. But it is also a feature of zero-sum games that one player must win. But it's too early to say who yet.
Michael Barone,The Examiner's senior political analyst, can be contacted at email@example.com. His column appears Wednesday and Sunday, and his stories and blog posts appear on ExaminerPolitics.com.