I think you're creating all sorts of divisions where none really exist. There is NO substantive division between Democratic realists and Democratic internationalists and not much between them and their likeminded Republican brethren. The predominant strain of thought in American foreign policy since WW 2 has been liberal/internationalist/realist. It was conceived by Acheson/Marshall/Kennan/
Harriman et al. and pursued by every administration, Republican or Democrat, from then until 2000. Separate this from domestic political posturing, and apart from minor shading the policy differences of Acheson, Dulles, Rusk, Kissinger, Shultz and Albright are indiscernible. Essentially, it consisted of enlightened self interest pursued through containment of adversaries; operating through international institutions wherever possible; and the fostering of alliance systems. On the whole it was a fairly respectable endeavor although there was dirty dealing from time to time. Occasionally, the bus would come off the road of course, notably over Vietnam, and Jingoism or the military lobby would get the upper hand, but it seldom lasted long.In 2001 there really was a quantum shift in policy to one of overt interventionism; rejection of traditional international institutions as a problem solving mechanism; disinterest in the views of major allies; open support of the most extreme Israeli positions in the middle east; and the embrace of attempts to export democracy, even if in a somewhat ham handed way. This whole approach was increasingly dominated by domestic political considerations, perhaps that was its original genesis, and it has proved fairly disastrous in almost every respect ...Now with the election of Democratic administration the inevitable reaction has set in and the Republican internationalist/realists are anxious to get back in their traditional groove alongside the folks who think the same way in the Democratic party ... you and Yglesias are quite wrong, this state of affairs is sustainable for a very long time. Any fault lines that appear are far more likely to be between a Lugar and a Cheney than between a Lugar and a Clinton. There are no fault lines between a Daschle and a Clinton. I use these names, but this is not really a matter of personalities despite the media's obsession with people rather than substance.
I think thus is rather like Robert Kagan's suggestion last year that we are all neocons of some sort or another: It emphasizes important commonalities - in this case, among post-WWII internationalists of various sorts, especially during the Cold War - but elides extremely important differences in order to make its case. Saying "the predominant strain of thought in American foreign policy since WW 2 has been liberal/internationalist/realist" is like saying that "the predominant strain of thought in American domestic policy since WW 2 has been liberal/neoliberal/neoconservative." It gets at the important point that policymaking has operated within a more constrained range than many people think, but it obscures the fact that there are very important differences between domestic-policy neoconservatism and domestic-policy liberalism - or between, say, the realist internationalism of Dwight D. Eisenhower and the liberal hawkery of John F. Kennedy. (Just compare this speech to this speech ...) The latter set of differences manifested themselves most notably in our policy toward Indochina - and if your case that the Iraq War represents a unique break with five decades of unbroken foreign-policy consensus requires dismissing the years America spent embroiled in Vietnam as a case where the bus went "off the road" modestly but not for long, you're probably overselling your argument a bit.