Maybe I’m just getting older, but I can’t really recall any person or persons in the current political landscape of the United States who is regarded as a truly seminal thinker or important philosopher with respect to the future political or social direction of the US.
No one really seems to have a truly* different* idea re what we should be doing politically or socially. We’re all just arguing over tweaks in the machine.
Do these people exist? If so who are they?
Is that a bad thing? I’d say we do have social commentators who do make a difference, but think of it this way:
Of course these people exist. They just aren’t limited to white guys at the lectern.
There’s the New America Foundation, a/k/a “Silocon Valley’s Think Tank.” See The Radical Center, by Ted Halstead and Michael Lind.
Are we talking about people who truly are outstanding political thinkers or just people who are often considered to be such?
Because there are a good number of people who consider Sarah Palin and Glenn Beck to be outstanding political thinkers, despite the evidence that they aren’t.
Even though the abundance of the second type might explain the lack of the first.
What are some people from the past that you would consider examples of what you are looking for? Over the last few decades, several political theorists have come out of the US who have done groundbreaking and innovative work, like Rawls, or Nozick, or Butler. But I’m not sure if they qualify. While they are leading voices in the academic world of political theory, they have not come out tried to politically mobilize people behind their views (although Judith Butler has supported the Occupy movement and has spoken at Zuccotti Park) and their work probably goes unnoticed by the vast majority of even those that are really interested in politics, as often it has little discernible bearing on the day-to-day of politics.
Noam Chomsky would fit that bill.
Maybe he would for the OP, but Noam Chomsky is not a political theorist in an academic sense and I don’t think political theorists or people in philosophy departments take his work seriously. His linguistic work, perhaps, but not his political work.
The linguist? 
Charles Taylor comes as close as anyone, I think.
Ah. A communitarian. But a Canadian – the OP asked for Americans.
Hmm… thought I’d be covered up with suggestions. Looks like a pretty barren intellectual landscape for a nation of 300+ million people that prides itself on being an advanced country. Oh well.
I clicked the thread to mention Noam Chomsky, and I’m glad someone beat me to it to deflect some of the trite ridicule. Any Doper tired of the sound of one hand clapping might do well to take time off from GD and read one of his political books.
Although best noted for his linguistics, Mr. Chomsky is an important thinker on other matters. Wikipedia writes of him:
Some of those ridiculing Chomsky as an “intellectual heavyweight re social & political philosophies” are probably describing David Brooks as a “leading intellectual” in another thread. :smack: :smack: 
:o Getting deeply into political theory as such is traditionally more of a Euro thing. Continental Euro – even the Brits lag behind in it, as I understand. We Americans know we have the best system imaginable, so why look any wide or deeper?
I do know of one American who thinks otherwise, intellectual heavyweight or not: Lefty Daniel Lazare, author of The Frozen Republic: How the Constitution is Paralyzing Democracy. It’s well worth a read, lots of unusual historical perspectives. But, he’s the sort who believes we would surely have some kind of socialism or social democracy in America by now, if the Constitution did not get in the way, as it was blindly or perniciously designed to do. Michael Lind disputes this, and I’m inclined to agree that we just don’t have a social-democracy-seeking electorate and never have had. (Someday, maybe.)
It’s not barren at all. The most interesting political theorists at the moment are not necessarily public intellectuals. Modern American political theory also tends to be quite analytical. It’s a bit less accessible than the Federalist Papers. Many of the problems are also technical, or as you might say, tweaks to the machine. I don’t think this is a fair criticism, but is very likely how you would see it.
Political theory was all but dead in the US until Rawls’ Theory of Justice in 1971. Ever since then, much of political theory is in some way a response to Rawls. Just look at the criticism section on wikipedia. A lot of high octane thinkers (Arrow, Harsanyi, GA Cohen, Sen, Nozick, Sandel) have been grappling with Rawls for decades.
Amongst academic geographers, we lost a good one when Allan Pred passed away a couple of years ago. David Harvey has lived and taught in the US for decades, but I believe he’s British-born. Derek Gregory is Canaduan, I think. Does Donna Haraway consider herself a geographer? Anyway, she might fit your bill. Also the previously mentioned Judith Butler. Zygmunt Bauman? Oops, no, he’s Polish-born, living in England.
The U.S. has grown fat and complacent and, as Tocqueville observed, its pragmatism, materialism, and egalitarianism were never truly hospitable to the kind of leisurely reflection and aristocratic temperament necessary to produce profound philosophical thought.
You’ll have to look elsewhere to find people who are trying to think beyond the liberal democratic capitalist order. For me, one of the more interesting is Alain de Benoist. His books are slowly being translated into English, so hopefully he’ll find a larger audience. You might wish to start with The Problem of Democracy and Beyond Human Rights. If you can read French, his website offers a wealth of additional articles and books.
That’s one opinion.
Plato was an aristocrat, and his philosophy sucks.
As far as I can see this is a bunch of nonsense. Liberal democratic capitalism is based on the philosophical (and political and economical) though of men like John Locke, Edmund Burke, and Adam Smith. New philosophical thought (rather than refining and improving old ones) only occurs when there is a fundamental flaw or crisis in the current philosophy.
Did you name yourself after this fellow BTW: http://en.wikipedia.org/wiki/Arthur_de_Gobineau