One graduated from Baker High, a public school in Columbus, Ga.; the other from Cranbrook, a private school in Bloomfield Hills, Mich. One has a Ph.D. in history from Tulane; the other has an MBA from Harvard. One steeped himself in the details of the colonial educational institutions of the Belgian Congo; the other in the minutiae of failing companies in the United States.

One almost always wears a tie in public; the other increasingly is abandoning his Brooks Brothers gray suit and crisply knotted rep tie for the sort of dress-casual look you might see dockside at the cocktail hour or on campus for the tailgate just before the Princeton game. One is extemporaneous, the other scripted.

One has been in politics for more than a third of a century; the other only for half that long. One went to France as a young man to explore the battlefields at Verdun; the other as a missionary to win converts. One worked for Nelson Rockefeller in the 1968 Republican presidential nomination fight; the other supported George Romney. One can tell you how many Catholic-school teachers were in Leopoldville, the other how many employees each Staples outlet needs.

One delighted in obliterating the Republican power elite; the other is a direct blood descendant of the GOP establishment. One thinks out loud, tossing ideas around like political-convention confetti; the other is careful and deliberate, with nary an impulsive remark. One lacks discipline; the other lacks spontaneity.

Nothing in common

This is what the Republican presidential nomination fight has come down to: a struggle between two men who have almost nothing in common, who have different temperaments and outlooks, who have divergent views of the origins and nature of conservatism, who personify two streams of the modern Republican Party, the incendiary, rootless radicalism represented by Newt Gingrich, the historian with contempt for the Republican past, and the respectable, Midwest-rooted, business-oriented strain represented by Mitt Romney, the businessman whose style grows out of the GOP past.

There hasn’t been a nomination fight like this since 1964.

To be sure, recent nomination struggles have featured battles between regulars and insurgents. Ronald Reagan, the supply-side, small-government apostle from Hollywood, took on Gerald Ford, the very model of the post-New Deal get-along Republican lawmaker, in 1976, and George H.W. Bush, the striped-pants son of a senator with a Wall Street partnership, in 1980. Gary Hart, the new-ideas senator from the ascendant Mountain West challenged Walter F. Mondale, the established personification of the New Deal coalition and Minnesota liberalism, in 1984.

Identity and ideology

Both of these fights involved urgent questions of identity and ideology. Both represented divergent paths for the two parties. But neither of them involved the emotional antimatter and stylistic competition, contention and collision at the center of the struggle between Romney and Gingrich, deny it as both sides might.

The fight for the Republican nomination finally means something. A fortnight ago it seemed merely a prologue to the Republicans’ effort to defeat and repudiate President Barack Obama. It remains that, of course, but first the Republicans need to decide what sort of party they will have as they move into the 2012 general election.

The old tug-of-war between social and economic conservatives, which began to emerge as Reagan departed the scene, supplied part of the storyline of 2012. The Iowa caucuses were supposed to be the social conservatism sweepstakes, the New Hampshire primary the economic conservatism showdown, South Carolina would present a Saturday social conservatism encore, and then the party would get down to business 10 days later in Florida.

Gingrich changes race

But the rise and fall of a number of Romney challengers and the eventual emergence of Gingrich has changed all that. The NBC News-Marist Poll shows Gingrich ahead in Iowa and 16 points behind in Romney’s New Hampshire redoubt. The race is on for the former supporters of Herman Cain — Gingrich is the clear favorite there — and the character of the contest is altered immutably.

For a long time, Romney managed to make the GOP contest a referendum on other people while maintaining a steady but not overwhelming lead. Now that’s changed, too. Both Time (“Why Don’t They Like Me?”) and The New Republic (“You Won’t Like Him When He’s Angry”) last week released covers on presidential timber and temperament, treatment until now reserved for Gingrich, who has inspired stunningly little support for his personal style and character. It’s now Romney’s turn.

But portraying one as a prig with his nose in the air and the other as a pugilist who’s happiest busting his opponent’s nose isn’t getting anyone anywhere and returns the contest to issues and mechanics.

Romney is, or has become, a conventional 21st-century conservative, opposed to taxes, Obamacare and the notion that humankind has contributed to, or can alleviate, global climate change. Gingrich holds most of these views most of the time, but can be counted on grafting an unusual aside, or an acidic critique, onto his remarks. Romney would methodically undo much of Obama’s work; Gingrich would take on the task with relish and revenge.

Contrasting campaigns

Romney’s campaign was built the traditional way — slowly, deliberately. Gingrich’s was built the Gingrich way, with volcanic eruptions of energy and ideas, completely out of sync with the usual rhythms. His is a campaign so underfunded that former Sen. Rick Santorum has attracted more maximum $2,500 donors than Gingrich. His campaign is so underorganized that the candidate’s New Hampshire headquarters was open only 16 days when the state’s largest newspaper endorsed him last month for president. Ordinarily it’s too late to try to build an organization a month before Iowa and too dangerous to float dramatic new ideas a month before New Hampshire. Gingrich is challenging not only conventional ideas about policy but also conventional cadences of politics.

But in the last few days this has also become a deeply personal struggle for each man’s legacy. If Romney, a former Massachusetts governor, loses, he’s a footnote in history, not even a William G. McAdoo or a George Romney, both of whom aimed at the presidency twice and are largely forgotten today. If Gingrich, who ended four decades of Democratic House control, loses, he’s still a historic figure. It’s a fight for the ages, and for the future.