Mr. McElvaine is a Professor of History at Millsaps College. His latest book, Grand Theft Jesus: The Hijacking of Religion in America, will be published by Crown in March.

There is nothing new about insurgent presidential candidates. The Democratic party seems to have one every four years. But it has become clear that there is something very new about this year’s insurgent, Sen. Barack Obama. The difference can best be seen in mathematical terms: the Obama campaign is making a serious attempt to change the type of math by which American politics has been calculated for the last 40 years.

The Republican era that began with the election of Richard Nixon in 1968 was based on a politics of division. Vice President Spiro T. Agnew called it “positive polarization—to divide on authentic lines,” and Republican strategists from John Mitchell through Lee Atwater and Karl Rove have pursued this political mathematics of division ever since. The basic idea was well summarized by a young Patrick J. Buchanan in a memo to President Nixon: “Cut . . . the country in half; my view is that we would have far the larger half.”

The most revolutionary thing about the Obama approach when compared with the political math of the last four decades is that the Obama new math is based on the politics of multiplication instead of the politics of division.

The political math of the past four decades has been based on subtraction as well as division. Karl Rove’s math sought to subtract as many voters as possible from the electorate through negative campaigning. This approach subtracts voters from both sides, but is designed to subtract more from the other side, thus leaving an inequality with fewer votes on the other side. Rove also made no attempt to gain much more than half of those who would be left voting. Us=51%; Them=49% was fine with him.

The political math of division and subtraction through polarization may have been positive for the party and candidates engaged in them, but the quotient and remainder were plainly negative for the nation.

Obama’s new political math uses a plus sign in place of the minus sign that has been used in recent decades. It attempts to be positive instead of negative. Equally important, the mathematical operation it seeks to accomplish is voter addition instead of voter subtraction—working to expand the electorate instead of trying to contract it.

The last candidate who practiced the sort of political multiplication Obama is attempting was Robert Kennedy in 1968. Following his assassination that year, political multiplication was displaced by political division. Republicans have been running against the Sixties for 40 years. Richard Scammon and Ben Wattenberg pointed the way in their 1970 book, The Real Majority, in which they noted that the American majority was “un-young, un-poor, [and] un-black.” Division of the nation by running against those “Sixties” groups was the way to win.

Coming from a new generation, Obama is trying to put the divisions that arose in that decade behind us. He is attempting to inspire people to expand the electorate instead of dispirit people to shrink the electorate.

The potential of replacing political division and subtraction with multiplication and addition has been evident in the early contests for the nomination and was particularly apparent in South Carolina last Saturday—as it could be across the South and the nation in November if Obama is the nominee. The huge turnout for the Democratic caucuses and primaries has shown what can happen when the people who had been subtracted from the electorate, especially minorities and young people, are instead added.

In South Carolina, Barack Obama not only received more than twice as many votes as Hillary Clinton; he also got twice as many as John McCain had won in that state’s Republican primary. Political multiplication and addition might expand the electorate to the point where it can turn solidly red states blue.

Since the late Sixties, successful politics in the United States has been based on a simple mathematical/political formula: Divide and conquer. Sen. Obama is attempting to win by using the inverse formula: Unite and conquer

The greatest difference between the Obama campaign and that of his leading Democratic opponent is that Sen. Clinton has been pursuing the nomination through the old math of division, as became all too clear in the tactics of her husband in recent weeks.

Democratic voters this year have a choice between two types of political mathematics and two types of unifiers.

Although Sen. Clinton has used the old political math of division, both she and Sen. Obama are unifying figures. Obama offers an opportunity to unify the fractured American nation. Sen. Clinton offers an opportunity to unify the fractured Republican Party, which will use her as the divisor to split the nation yet again.

The choice for Democrats is clear: They can use the new political math of multiplication to transform the Disunited States of America back into the United States of America and leave the disunited Republican Party divided, or they can continue to use the old political math of division within their party to transform the disunited Republican Party back into the united Republican Party and leave the Disunited States of America divided.

MS. NORRIS: I mean, they [the Republicans] actually will talk openly about bringing Barack Obama down a few notches because they want to run against Hillary.

MR. MEACHAM: Because it's a known known, to give Secretary - former Secretary Rumsfeld his due. Hillary Clinton, they know what to do. Barack Obama, how do you run against the first African American nominee? It explodes all conventional campaign dogma in ways that completely will surprise and pleasantly and unpleasantly perhaps as they go forward. And I that that that's the - one of the things that's so scary about Obama to Republicans is they don't how to run against him. (my emphasis)