Cartoonist Randall Munro of XKCD.com offers this, under the heading "Poll Watching"

But in fact, our poll analysis Romney's Unreported Share of the White Vote will continue after the election, whoever wins, based on exit polls.  That's how we get figures like those in the table below:

These are the shares of the white vote garnered by recent GOP Presidential candidates.

Nixon	1972	67%
Ford	1976	52%*
Reagan	1980	56% [1]
	1984	64%
Bush I	1988	59%
	1992	40%* [1]
Dole	1996	46%* [1]
Bush II	2000	54%
	2004	58%
McCain	2008	55%*

 

(* = defeated.  [1] Major Third Party ran.)