The hypothetical horse race leading up to the 2008 presidential election has so far ignored the pivotal influence of the fastest-growing group of voters in America – independents.

Over the last 10 years alone, their ranks have increased almost 300% in states that register voters by party. This massive rejection of politics as usual has been papered over by Karl Rove’s play-to-the-base strategy and Howard Dean’s manic equal and opposite reaction. But if the two parties insist on rejecting independent voters by nominating polarizing conservative and liberal candidates, 2008 could be the year that a strong centrist independent is elected president as part of a bipartisan national unity ticket. It is an unlikely but not at all impossible scenario.

For example, if the Democrats cannot resist the temptation to nominate Hillary Clinton, and establishment social-conservative pull their strings in the primary to put the Senate majority leader, Bill Frist, on the ballot, a large number of moderates from both parties and independents would demand an alternative. The Democrats so far lack a national candidate who commands respect across party lines, but Republicans have both Mayor Giuliani and Senator McCain.

Not coincidentally, Messrs. Giuliani and McCain are consistently the two leading candidates among Republicans and voters nationwide in the Marist poll. They campaigned tirelessly for President Bush in 2004 and are working to build bridges within their party, but they are bitterly opposed by some members of the far-right for being too moderate. The key question of the 2008 election will be whether this minority will be able to exert an effective veto before the general election.

The two-party system is set up to make successful independent candidacies difficult. Such a campaign would be few serious candidates’ first choice – it is far tougher to win the presidency without the existing infrastructure of a party. But with Americans offered a variety of choices in every other aspect of their lives, being required to choose between the lesser of two evils in elections is losing its common sense relevance.

The two parties like to dismiss or distort the growing number of independents because it makes their job easier. To this end, states don’t have consistent rules regarding party registration, and in many states voters are lumped in as unaffiliated if they ask to be registered as independent. Regardless, taken as an aggregate, the shift toward independents is startling, even in the politically saturated opening states of the presidential primary contest.

In the first caucus state of Iowa, 38% of all voters are now not registered with either the Democratic or Republican party, while in the pivotal first primary state of New Hampshire, in which Mr. McCain beat then-Governor Bush by 19 points, 85% of new voters have been registering independent. South Carolina’s subsequent primary is notoriously conservative, but both Governor Mark Sanford and Senator Lindsay Graham backed the maverick centrist Senator McCain against the Republican establishment’s wishes in 2000 – and their influence has only advanced in the intervening years.

A glance at the shifting election demographics nationwide gives a good sense of how grassroots politics in the information age have shifted even as the parties stick to the old industrial age playbook.

In the nation’s fastest-growing and most populous state, California, the Democratic Party lost 7% of its registered voters over the past four years and the Republicans lost 5%, while the ranks of independents increased 30%. In the archetypal battleground state of Florida, the number of unaffiliated voters has increased to almost 1.9 million today from 527,000 in 1994. Likewise, in Pennsylvania, independent voters have increased to 925,000 in 2004 from 381,000 in 1994. In New Jersey, unaffiliated voters now make up 58.7% of the electorate. This trend is evident in the shifting face of the South as well – in North Carolina, the number of unaffiliated voters has increased to well over a million in 2004 from 294,000 in 1994. It can also be seen in the Southwest, where independent voters in Arizona have grown to 655,000 from 214,000 since 1994. In addition, 41% of college undergraduates are self-identified independents.

In the next election cycle of 2006, at least two potentially significant gubernatorial candidates are planning to run as independents – Virginia state senator Ross Potts and Texas’s country musician turned comic novelist Kinky Friedman, who has brought on the campaign manager of Jesse Ventura’s successful 1998 independent campaign to serve as governor of Minnesota.

In the new issue of the Atlantic, James Fallows writes a cover-story memo to a 2016 front running third-party presidential candidate, driven to office by a political dynamic described as: “Democrats can’t win, and the Republicans can’t govern” – especially on the issue of fiscal responsibility, which in this futuristic scenario has led to protracted economic depression. It recalls circumstances that spurred the last serious independent candidacy for president by Ross Perot in 1992. Mr. Perot called together a broad coalition of fiscal conservatives, government reformers, and Republicans nervous about the growing influence of the religious right. He led both Bill Clinton and then-President Bush in polls before briefly dropping out and then stumbling back into the race, finishing with 19%.

This original one-fifth of the electorate and its growing number of inheritors are still politically homeless – in fact, their grievances have gotten worse.The party that reaches out to them can realign politics to their benefit for decades to come. But if they fail, in the name of playing to their base, they may unleash a profound backlash and series of events that ushers in a new era in American politics.