How can the idea of identity (or sameness) vs. difference in American politics be analyzed.
I would argue that a great deal of (I might even say almost all of it) American politics involves attempts to define who is the same as "us" and who is different. People of both political parties tend to try to say that those who agree with them are "self" -- they are real Americans while those who disagree with them are in some way "other" -- they are fundamentally different from "us."
I would argue that you can see this in the way that many conservatives talk about Pres. Obama. They tend to emphasize his middle name, for example, and to try to portray him as insufficiently American. They do not simply say that they disagree with him. Instead, they try to identify him as "other" -- as fundamentally non-American.
You can also see this to some extent in the rhetoric surrounding the governor of Wisconsin's efforts to kill public employee unions in his state. The Democrats are portraying his efforts as an attack on regular, middle-class Americans. They are not portraying it as simply a political maneuver -- it is an attack on real Americans and their way of life.
So, I would argue that much political rhetoric today involves trying to argue that those who disagree with "us" are in some way fundamentally different and unAmerican.