Yglesias says:

The crux of the matter is that while truly conservative foreign policy thought has a long history of wrongness in the United States it’s rarely genuinely held sway on the big issues. Presidents Eisenhower, Nixon, and Reagan all at key moments broke with elements of their conservative base to preserve containment, to initiate détente, to continue with the bilateral arms control process, etc., leaving run-amok rightwingery mostly to fester in third world battlefields rather than on the central point of America’s relationship with Europe, Japan, and the Soviet Union.

A lot hangs on that adverbial, since a large part of the argument that some of us have with movement conservatives is whether or not the foreign policy they espouse is “truly conservative.”  One important test of whether foreign policy is truly conservative, rather than nominally or conventionally so, is whether it actually achieves conservative ends, or if it is a fundamentally reckless, imprudent, unwise and destructive approach to international relations.  I won’t dispute that there has always been a strain within the movement that has believed not simply in strong defense but has degenerated into a reflexive desire for confrontation, and unfortunately I think that this strain is still predominant.  Using the appeasement trope is just one sign of the confrontational mode that many on the right mistake for foreign policy thinking, but I fear it may be an integral part of the nationalism that many on the American right have embraced all along, which leads to the identification of the nation with almost every commitment and deployment overseas that the government undertakes that then makes the possibility of negotiation in the context of those foreign deployments unthinkable.  If nationalism makes many American conservatives unwilling to resist or oppose these commitments and deployments, I suspect it also makes them extremely hostile to anything that resembles hedging on those commitments or withdrawing from a region, because these can be likened to the “appeasement” of the 1930s.

To return to Lukacs yet again:

They were nationalist rather than patriotic: they put their nationalism above their religion, their nationalism was their religion.  Thus American conservatives welcomed (at worst) or were indifferent (at best) to the dangers of excessive American commitments to all kinds of foreign governments or—what was more important—to the flooding of the United States by countless immigrants from the south who would provide cheap labor but whose increasing presence could only exacerbate deep national problems.  There were many Catholics among the conservatives; but their publications would criticize popes and bishops when the allocutions of the latter did not coincide with the desiderata of their ideological nationalism.

So it is not at all clear that the confrontational policies over the years of “rollback” or “rogue state rollback” or “pre-emptive war” (i.e., aggressive war) supported by many on the right were, are, “truly conservative,” but they may find their origins in the nationalism that many American conservatives hold.  Yglesias would probably say that this is an irrelevant point, but for conservatives that is the real crux of the matter.