Rethinking Overton
Personally, I think that the concept of a two-dimensional window to describe the Overton window is rather short-sighted. It simplifies politics and causes to brutish left-right and liberty-authority dichotomies. I prefer to think of it as a porous sphere, with infinite directions on which it can be acted, and political entities, causes, and even people are all minute parts surrounding it, both on the inside and out. Different, often static entities act on this bubble, both pushing it from the inside, and pulling it from the outside, in an attempt to either keep themselves inside, earn their way inside, or guide it so that undesirables end up out of it.
Those entities do not act alone, though. They are similar to a spider's web, all connected by various ties, both through the bubble, within the bubble, and outside of it. And through those ties, each of those entities pulls at one another, ensuring a certain sense of stasis, unless the ties happen to sever. And, since tension is a set of forces pulling at an object from various directions to keep it taut, occasionally those ties break, or new ones form that guide an entity into a particular direction, sometimes within the bubble, or even guiding it outside of it.
Naturally, not all pulls are created equal. Those within the bubble tend to have more gravity than those on the outside. Media and establishment backing are very effective and powerful tools to ensure that the bubble stays just where those on the inside want it. The status quo, after all, is a remarkably powerful lobby. Also, being a web rather than a line means that multiple forces may act upon one entity at any given time, creating pulls in various directions, and potentially heightening the tension between the entity and another one to unsustainable levels. Politics, after all, involves myriad interconnecting interests, all of which influence one another in very subtle manners.