One graduated from a public school in Columbus, Ga., the other from 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 delighted in obliterating the Republican power elite; the other is a direct blood descendant of the GOP establishment. One lacks discipline; the other lacks spontaneity.
This is what the Republican presidential nomination fight has come down to: a struggle between two men who have almost nothing in common. They have divergent views of the origins and nature of conservatism, and they personify two streams of the modern Republican Party.
The incendiary, rootless radicalism is represented by Newt Gingrich, the historian with contempt for the Republican past. The respectable, Midwest-rooted, business-oriented strain is 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.
Recent nomination struggles have featured battles between regulars and insurgents: Ronald Reagan versus Gerald Ford and George H. W. Bush in 1976 and 1980, Gary Hart versus Walter Mondale in 1984.
But neither of these battles involved the emotional anti-matter and stylistic competition, contention, and collision at the center of the struggle between Mr. Romney and Mr. Gingrich.
The fight for the Republican nomination finally means something. A fortnight ago, it seemed merely a prologue to Republicans' effort to defeat and repudiate President 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 campaign.
The old tug of war between social and economic conservatives, which began to emerge as Reagan departed the scene, supplied part of the story line 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 social-conservatism encore, and then the party would get down to business 10 days later in Florida.
But the rise and fall of a number of Romney challengers and the emergence of Mr. Gingrich have changed all that. An NBC News/Marist Poll shows Mr. Gingrich ahead in Iowa and 16 points behind in Mr. Romney's New Hampshire redoubt. The race is on for the former supporters of Herman Cain -- Mr. Gingrich is the clear favorite there -- and the character of the contest is altered immutably.
For a long time, Mr. Romney managed to make the GOP contest a referendum on other people while he maintained a steady but not overwhelming lead. Now that's changed, too.
Both Time magazine and The New Republic published cover stories last week on presidential timber and temperament -- treatment that until now was reserved for Mr. Gingrich, who has inspired stunningly little support for his personal style and character. It's now Mr. Romney's turn.
But portraying one as a prig with his nose in the air and the other as a pugilist who is happiest busting his opponent's nose isn't getting anyone anywhere, and returns the contest to issues and mechanics.
Mr. Romney is, or has become, a conventional 21st-century conservative, opposed to taxes, Obama-Care, and the notion that humankind has contributed to, or can alleviate, global climate change.
Mr. Gingrich holds most of these views most of the time, but he can be counted on to graft an unusual aside, or an acidic critique, onto his remarks.
Mr. Romney would methodically undo much of Mr. Obama's work. Mr. Gingrich would take on the task with relish and revenge.
Mr. Romney's campaign was built the traditional way -- slowly, deliberately. Mr. Gingrich's was built the Gingrich way, with volcanic eruptions of energy and ideas, completely out of synch with the usual rhythms.
Mr. Gingrich's campaign is so underfunded that former Sen. Rick Santorum has attracted more $2,500 maximum donors than Mr. 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 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. Mr. Gingrich challenges not only conventional ideas about policy, but also conventional cadences of politics.
In the past few days, this has also become a deeply personal struggle for each man's legacy. If Mr. Romney, a former Massachusetts governor, loses, he's a footnote in history. If Mr. 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.
David Shribman is executive editor of the Pittsburgh Post-Gazette.
Contact him at: email@example.com