the link to the article by J.K.Galbraith I gave above perfectly answers itGalbraith isn't a political scientist. He's a well-respected economist, like Krugman, who writes political commentary. That's nowhere near the same thing. One may as well call Rush Limbaugh a political scientist.
One will also note that you complained that while America has citizens on the Left, these people do not have representation. You then went on to use Pres. Obama as an example of this. Let me remind you that the President isn't intended to be a representative of anyone: his job is to execute the decisions of the Congress and of the Courts. Thus, blaming him for what those decisions are is nonsensical.
I don't wish to actually debate the topics you list, but I'd like to briefly address a couple of them -- not in the interest of proving that I'm right, but to show that there really are (at least) two sides to these stories, and that the ideas of the Left really are being represented.
I understand that the Left feels betrayed by the recent debt ceiling deal. But you should understand that fiscal conservatives feel precisely the same way. Contrary to the hyperbole in the media, there really are no cuts to spending: by and large, the cuts agreed on are doing nothing more than slightly slowing the projected growth of spending. The decreases you'll see in spending next year are, quite literally, a drop in a bucket. To say that such a trivial compromise is caving in to the Right is disingenuous.
I'm not sure what you mean when you say that Obama (for which I'm substituting "the Democrats of Congress, since, as I noted above, it makes little sense to hold the President accountable for the actions of Congress) betrayed the Left over healthcare. I mean, we've now got a system in place that will guarantee medical care to everyone. This certainly is not the outcome that the Right wanted. Indeed, since it seems that a majority of Americans today dislike it (or at least the way it was implemented), there must be some force to the left of center that dragged it in that direction.
There is one area where I do think you've got good reason to feel betrayed, and that's all of our various wars. Back in 2008, the Democrats took a clear stand against our wars -- Iraq and Afghanistan -- and make all kinds of promises to get out. Yet today, we're still fighting, and although troop levels are lowered, there's really no actual end in sight. But, to make matters worse, Pres. Obama has illegally gotten us tangled in another war (in Libya), and Congress -- both the DEMs and the GOPs -- have done nothing to stop it.