If you are, understandably, already somewhat fatigued from trying to make any sense of the ups and downs, to say nothing of the ins and outs, of the marathon presidential campaign we are now embarked upon, this column contains valuable information that, at the minimum, can save you hundreds of hours of time and energy over the next 18 months while simultaneously establishing you as the political guru of your carpool and/or poker club.

Ignore all the "inside baseball" rumors about which lieutenant governor of what small state intends to endorse what presidential candidate. It does not matter. Pay no attention to whether the party's direct-mail wizard has either quit or joined the dark horse candidate's campaign. It does not matter. What does matter — in predicting who will be chosen the 2008 Republican presidential nominee at the GOP Convention, which meets in St. Paul, Minn. on Sept. 1, 2008 — is which candidate leads in the Gallup poll conducted on or around Sept. 1, 2007.

You say you want proof? Consider this: In the last 14 presidential elections, the Republican presidential candidate who led for the nomination in the Gallup poll conducted closest to one year before the Republican convention did become, 12 months later, the presidential nominee.

That's right. George W. Bush was running first in the summer of 1999, just like Bob Dole was the leader in 1995, and in 1987, George H.W. Bush was the Republican front-runner. Before that in 1979, Ronald Reagan was first. In 1975, it had been Gerald R. Ford, and in both 1967 and 1959, Richard M. Nixon was the first choice of Republicans for the next year's presidential nominations. In 1963, the Republican presidential numbers fluctuated, but by one year out, Barry Goldwater had moved into first place. In 1951, it had been Ike in first place. It goes without saying that in 1957, 1971, 1983, 1991 and 2003, incumbent Republican presidents were the overwhelming Gallup leaders for re-nomination.

History, in sharp contrast, is of no guidance in predicting Democratic presidential nominees. As political analyst Rhodes Cook recently observed: "Since 1972, George McGovern, Jimmy Carter, Michael Dukakis, and Bill Clinton all won the party's nomination" even after registering a Gallup poll standing of 5 percent or less" in the year before the election." What makes that fascinating is that two of those long-shot underdog candidates who eventually were nominated — Carter and Clinton — are the only two Democrats elected to the White House in the last 44 years.

Being the Democratic front-runner 12 months before the nominating convention has been no bargain. Front-runners included Edmund Muskie in 1971, Edward Kennedy in both 1975 and 1979, Paul Simon in 1987, Mario Cuomo in 1991, and Joe Lieberman in 2003. None became the nominee. In the last half century, only three non-incumbent Democratic presidential nominees led in the poll closest to one year before the nominating convention: John Kennedy in 1960, former vice president Walter Mondale in 1984, and sitting vice president Al Gore in 2000.

The Republicans are more like the Rotary club. If you're recording secretary, this year, you can expect to be sergeant-at-arms next year, and president two years after that. When I was covering the 1996 Iowa caucuses, I asked one dedicated party chair in Ottumwa why he was backing front-runner Bob Dole. His answer is one I have never heard from a Democratic county chairman: "It's his (Dole's) turn." One Republican friend explains it this way: "We're the royal party. We believe in orderly succession."

That cannot be said for the zany, unpredictable way Democrats pick their standard bearers. Somebody wanders into the back of the hall and Democrats seem to ask, "What's your name?" "Carter." "McGovern." "Clinton." "Kerry" … "Nice to meet you. Why don't you come right up front here and become our presidential nominee?"

What could upset the iron historical pattern predicting GOP nominees is the flurry of states seeking to move their 2008 presidential primary earlier to Feb. 5. As veteran Democratic wise-man Michael Berman has reported, as many as 21 states are considering moving their primaries forward. If anything near that happens, we would have a de facto national primary where the candidates' increased dependency upon the ability to raise enormous sums of money could, and probably would, play a decisive role.

But don't bet against the Gallup poll one year before the Republican convention. It's called the winner 14 times in a row, which is infinitely better than the record of any of us riding on the press bus.

To find out more about Mark Shields and read his past columns, visit the Creators Syndicate web page at www.creators.com.