Addendum/update (added Feb. 2012): This post at the blog U.S. Intellectual History points out that Winthrop's city-on-a-hill metaphor (mentioned below) and Reagan's "shining city on a hill" are both rooted in the same passage in the New Testament, Matt. 5:14-16: "Ye [i.e., Jesus's disciples] are the light of the world. A city that is set on a hill cannot be hid."
I'm not going to offer much instant reaction to the president's Afghanistan speech, as I'm supposed to be on a break and there are plenty of other places where you can find instant reaction. However, I would like to take note of one sentence that occurred toward the end of the speech that strikes me as somewhat unfortunate: "Like generations before, we must embrace America's singular role in the course of human events."
Many people may take this simply as boilerplate, but that would only underline how deeply the virus of American exceptionalism has taken root in the body politic. My paperback dictionary, which I just checked, gives the first substantive definition for "singular" as "outstanding, exceptional." But it is not, I think, necessarily true that the notion of the U.S. as exceptional is something that has been embraced without question by overwhelming majorities of Americans for generations, as Obama's line implies. Nor is there, as far as I can recall, much of anything in the country's founding documents that suggests or supports an exceptionalist view. John Winthrop's 'city on a hill' speech, as revived by Ronald Reagan (who added the adjective "shining"), is probably the most obvious of the available precedents, but I don't think the framers of the Constitution were paying much attention to Winthrop, assuming the 'city on a hill' reference even means what Reagan supposed it to mean.
Pres. Obama is a relatively young president, served by, as far as I'm aware, very young speechwriters, and probably not surrounded on a daily basis by many people with a deep knowledge of history. Often this turns out not to matter much, but on other occasions it does.
It once seemed that every so often, at least until 9/11 and its sequelae, a group of scholars would get together and bring out a collection of essays under a title like America as an Ordinary Country. In fact that was the exact title of a collection edited by Richard Rosecrance and published in 1976; its subtitle was "U.S. foreign policy and the future." The argument or implication was presumably that the experience of Vietnam meant that the U.S. could finally shed an exceptionalism that had proved more of a burden than a benefit. I haven't read the book, but I suspect that today's policymakers could do worse than have their aides get a copy for them and spend a couple of hours with it.
P.s. (Afghanistan-related): I saw the documentary film 'Restrepo' recently (on DVD). Worth seeing.