I know I said I was reverting to silence, but hey...one of the benefits of writing an obscure blog is being able to ignore one's own pronouncements.
I just skimmed through a piece by Michael Desch (published as part of a symposium in PS, available here), who uses a line from Louis Hartz's classic The Liberal Tradition in America to explain the continuity between the Bush and Obama counter-terrorism policies. There is in fact some continuity; indeed, in certain respects -- e.g., more use of special forces operations in various parts of the world, more use of drone strikes -- the Obama admin has taken a more 'pro-active' counter-terror line than the Bush administration. (On the other hand, the Obama admin has been less inclined to sacrifice civil liberties on the altar of counter-terrorism than the Bush people were.)
Hartz's book, published in 1955 (when he was in his mid-thirties), has had a long afterlife. Desch quotes a sentence about liberalism's finding non-liberal ideas "unintelligible" and the effect this has on foreign policy. (I confess to never having read Hartz's book; I have, however, read Robert Packenham's 1973 book Liberal America and the Third World, which uses Hartz to explain and criticize U.S. efforts to advance 'political development' in poor countries.)
As a postscript, it should be pointed out, to avoid possible misunderstanding, that Hartz was not using "liberal" mainly in the liberal-versus-conservative sense of contemporary political debate, but rather to refer to a basic set of ideas that go back to the Founding and that have been broadly shared across the American political spectrum.
P.P.S. For discussion of Hartz's career at Harvard, which ended with his early retirement from teaching in 1974, see Paul Roazen's introduction to The Necessity of Choice: Nineteenth-Century Political Thought (Transaction, 1990), his edition of Hartz's lectures on that subject.