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.
Likewise, the fact that two out of the three living "Establishment" foreign-policy hands on my emailer's list - Shultz and Kissinger - publicly supported the invasion of Iraq, which supposedly represented a "quantum shift" away from their steady stewardship and into crypto-Likudnik jingoism, ought to be a tip-off that the landscape of foreign-policy debate is rather more complicated than he suggests. To the extent that there was an over-arching consensus that bound together the (pretty different, in my view) foreign-policy approaches of John Foster Dulles and Henry Kissinger, it vanished with the Cold War, and the last two decades have sent members of every school of thought groping for new guideposts, a state of affairs that's produced strange bedfellows, peculiar political migrations (see Buchanan, Pat, or Hitchens, Christopher) and odd dissonances (compare Charles Krauthammer on Kosovo to Charles Krauthammer on, well, almost every foreign-policy crisis since). 9/11 and the Iraq War magnified this sense of dislocation, in a sense, first by temporarily forging a new interventionist consensus anchored by neoconservatives and liberal hawks and joined by many realists, and then by just as quickly unraveling that consensus, which has now given way to the (theoretically) united front of realists, liberal internationalists and progressives that's on display in the Obama Administration.
Maybe this unity will be permanent: Maybe Robert Gates (who, one might note, has been retained as a reward for his success implementing a strategy vocally championed by ... neoconservatives), Hillary Clinton and Susan Rice will establish a new consensus that lasts for years or decades to come, with neocons chattering their teeth out in the cold. But more likely, it will last right up until the first major foreign-policy crisis of the Obama years, at which point the sort of ideological debates you saw inside the Clinton Administration over issues ranging from Yugoslavia to Osama Bin Laden will flare up in new and different forms. (And no, pace my correspondent, it really isn't that hard to imagine scenarios in which Hillary Clinton and Dick Lugar - or, more aptly, Robert Gates - end up on the opposite sides of an issue.)
How these debates will shake out is anyone's guess. Certainly, it's easy to imagine short term alliances-of-convenience between realists and progressives, and between liberal hawks and out-of-power neocons. But it's also easy to envision debates that push realists and neoconservatives back into one another's arms, or at the very least, forge a new generation of realists who feel uncomfortable in the Democratic Party. Debates over nation-building, say, and humanitarian interventions. Or arguments over counterrorism policy - where, say, a Jack Goldsmith isn't ultimately on the same side as many of the people who have praised him for opposing the excesses of Cheneyism. Or (perhaps most importantly) the long-term debates over national sovereignty and global governance that Gideon Rachman brings up in his latest FT column. Ultimately, all the different sorts of internationalists just aren't on the same side about a lot of very important issues, and I suspect that a host of cleavages that are currently obscured won't take all that long to re-emerge.