Welcome to the GOP fight club. It's becoming increasingly apparent that a debate is brewing in the Republican party over foreign policy, one that will not be conducted politely over brandy and cigars in an oak-lined room but, rather, with knuckledusters. The latest sign was the dustup between New Jersey governor Chris Christie and Senator Rand Paul. Christie, in an effort to burnish his conservative credentials, which came into some contention when he became palsy-walsy with President Obama at the finish line of the 2012 presidential race, to the consternation of many on the right, has voiced his own disquiet at what he sees as backpedaling by the GOP about the battle against terrorism.

At an Aspen Institute forum, Christie said that libertarians such as Rand Paul are endangering American national security: “This strain of libertarianism that’s going through parties right now and making big headlines I think is a very dangerous thought."

Now Paul is striking back.

On Monday Paul said to Sean Hannity on Fox News,

It’s really, I think, kind of sad and cheap that he would use the cloak of 9/11 victims and say, I’m the only one who cares about these victims. Hogwash. If he cared about protecting this country, maybe he wouldn’t be in this "give me, give me, give me all of the money" that you have in Washington or don’t have and he would be more fiscally responsive and know the way we defend our country.

This debate is overdue. It gets to the core of what amounts to an identity crisis for the GOP. This past Sunday the New York Times featured a piece of mine that reviewed two excellent books—Those Angry Days by Lynne Olson and 1940 by Susan Dunn—on the debate over isolationism in the 1930s over entry into World War II. The historian Arthur Schlesinger, Jr., said that the debabte over intervention was the "most savage political debate in my lifetime," even more impassioned than ones over McCarthyism and the Vietnam War. Many on the left were opposed to intervention because they felt burned by the outcome of World War I when Woodrow Wilson promised the war to end all wars. Instead, the punitive Treaty of Versailles, which laid the groundwork for a new one, was the result. On the right a number of figures such as Charles Lindbergh became admirers of the Nazi movement. The Wall Street Journal stated in June 1940 that Hitler had "already determined the broad lines of our national life for at least another generation" and that there was no point in trying to challenge him. Fortunately, Franklin Roosevelt saw it differently.

Yet the debate over intervention was not entirely stilled within the GOP. After World War II the Robert Taft wing of the party was opposed to entangling alliances abroad such as NATO. Schlesinger, in an illuminating essay in the Atlantic in 1952, distinguished between left and right isolationism. Schlesinger argued that left isolationism was rooted in idealism about America, that it should serve as a model for the world. On the right he diagnosed a fear of the old world—the belief that America would become corrupted by its dark mores: "An image of Europe began to haunt the isolationist consciousness—an image of a dark and corrupt continent, teeming with insoluble feuds, interminable antagonisms; senseless and malevolent wars. Europe was morally and politically diseased and scabrous; and contact with it would bring the risk of fatal infection." What Schlesinger deemed the old "affirmative isolationism" gave way to "negative isolationism." Schlesinger also concluded that figures such as Senators Robert Taft and Joseph McCarthy were attempting to disguise their opposition to intervention abroad by backing anti-Communist witch hunts at home. (Still, as the case of Alger Hiss showed, there was some subversion in America itself, though Hiss never had any position of real consequence. And it was none other than Richard Nixon who believed Whittaker Chambers' accusations and exposed Hiss.)

In the end, the Taft wing lost out. It was the moment of the moderate, internationalist Republican such as Nixon. By 1952 had allied himself with Eisenhower. For decades the internationalists were at the helm of the GOP. Then came the rise of the neocons who supplied a more militant edge. The libertarian wing of the party had lapsed into desuetude. But over a decade after September 11, the debate is starting all over again over about the extent to which America should intervene abroad.

It is a debate, however, that the GOP is likely to find very unsettling, at least if it is conducted by Rand Paul and Chris Christie. Neither appeals fully to the party. The neocon wing is virulently opposed to the doctrines that Paul endorses, which is why Sen. John McCain spoke of "wacko birds." But at the same time, conservatives will also have a difficult time cottoning to Christie, who is in many ways the classic Northeast moderate Republican. Unlike many of his political ancestors, however, Christie is not a patrician figure who shrinks from a fight. He is a brawler. A divisive battle over foreign affairs does not loom before the GOP. It has already begun.

Image: Left: Flickr/Gage Skidmore. CC BY-SA 2.0. Right: Flickr/Bob Jagendorf. CC BY 2.0.