The axiom in recent presidential elections is that the left and right stay put, while the middle shifts just enough to determine the winner.
When the middle moved to the right, we got Bush; when it slid left, we got Obama.
What makes the 2012 campaign so intriguing — and frightening — is that it may be determined by two other elements: the far right and the far left.
The role of extremists — arch conservatives and progressives — is nothing new. They've always sought to move the needle in their direction and then, when push came to voting, rallied around the candidate of their party.
If they didn't, it was ruinous, as in 2000 when Ralph Nader mounted a third-party challenge from the left, causing the defeat of Democrat Al Gore.
So in 2012, which extreme group will rally and which will revolt?
The conservative right, increasingly bound to absolute positions and refusal to compromise, may be gaining enough strength to derail the Republican Party's chances in '12.
Two of its front-runners, Gov. Rick Perry and Rep. Michele Bachmann, are pitching a brand of extremism that works in primaries, but has far less chance of success in a general election.
The Wall Street Journal editorial board worries that Bachmann seems "less principled than opportunistic" and Perry has too much "muscular religiosity" among other negatives.
It dismisses Mitt Romney as simply "weak," and wishes that "someone still off the field will step in and run." That someone would presumably be less beholden to the extreme right, perhaps New Jersey Gov. Chris Christie, who is said to be reconsidering entering the race.
Meanwhile, although President Obama has nothing to fear in the nominating process, he is being pecked by progressives. Vermont's Bernie Sanders, the Senate's most liberal member, said recently it would be a "good idea" if Obama faced primary challenges.
Iowa Sen. Tom Harkin called upon progressives to be more outspoken in criticizing the president.
Some liberal talk-show hosts and opinion writers are even less restrained in showing anger, claiming that Obama hasn't done enough to retain the support of those who worked so diligently on his '08 campaign.
Compared to the far right, however, which has virtually captured the policy-making wing of the Republican party, the far left is fragmented and has limited influence.
The true objective in presidential politics is to elect a party rather than a person. Idealists on both edges wish that were not the case. They hate giving ground to candidates and causes that don't fully measure up to their vision.
What should worry the Republican Party is that its extreme right has been emboldened by no-holds-barred, no-chance-of-compromise positions.
Tim Pawlenty, once thought to be a serious GOP contender, said as he abruptly dropped out, "I brought a rational, established, credible strong record of results, but the audience was looking for something different."
Pawlenty is conveniently ignoring his underwhelming performances in two debates, but his assessment of those currently crafting the Republican message is spot on.
What should worry Democrats is that the far left has been discouraged, if not paralyzed, by Obama's failures — despite the fact that most were caused by Republican obstructionism.
A half-hearted campaign effort by disillusioned liberals could be enough to tip the election the wrong way.
Progressives wish for a president who would speak more forcefully on controversial issues without worrying so much about appeasing the other party. Conservatives wish for a president who could be unyielding on issues that have stirred so much anger within their ranks.
As 2012 draws near, both extreme factions should be careful what they wish for.
Peter Funt is a writer and public speaker. He is also the long-time host of “Candid Camera.” He can be reached at www.CandidCamera.com. This column is distributed exclusively by Cagle Cartoons, Inc., newspaper syndicate.