If you think of the entire political spectrum as a football field …, the entirety of American politics is played between the 40 yard lines.
[Ed.] In attempting to source the commenter’s reference, I found this similar quote at the Seattle Times, “Politics Between the 40-Yard Lines” (November 13, 2006): “As has been the case for decades, American politics continues to be fought between the 40-yard lines. The Europeans fight goal line to goal line, from socialist left to the ultranationalist right. On the American political spectrum, these extremes are negligible. American elections are fought on much narrower ideological grounds. In this election, the Democrats carried the ball from their own 45-yard line to the Republican 45-yard line.”
I suspect there is a more original source.