A Massive Shift

I'm slowly putting together in my mind some arguments about changing political alignment and labels in America. The number of articles and essays that have been written lately about the Republicans (as abandoning their traditional platform, or as not actually being conservative) and the Democrats (as being reactionary, or hijacked by special interests), and the role of Progressives (whatever they are) in all of this point towards some dilemma or contention in American politics. As I put all this together, I'm kind of stuck on a question that a Professor recently asked me.

Margaret Thatcher could slam down a copy of some Hayek book and say "this is what we stand for." For conservatives, Friedman and Hayek define much of their philosophy.
Is there a leftist/liberal/progressive equivalent?
I'm inclined to say that the nature of the left is antithetical to adopting a doctrine. I'm also going to admit I'm not that well-read.