Dave Weigel writes in Slate :
COLUMBUS, Ohio — As I head to Republican victory headquarters, here's the starter kit.
National exit polls  from 2008.
National exit polls  from 2004.
74 percent: The white proportion of the 2008 electorate. If it's higher this time, it's good for Romney. Sorry, folks, it just is.
31 percent: The proportion of the Hispanic vote that went to John McCain. If it's stuck there, or lower, for Romney, it's terrible news in Nevada, Colorado, and Virginia.
+7: The raw Democratic advantage in the 2008 election. In 2004 and 2010, there was no Democratic advantage—it was tied. If there's a Democratic advantage of 3 points or more, even considering all the moves voters have made and the regional party differences, it indicates an Obama comeback.
- 46 percent: The proportion that Barack Obama won of the white vote in Ohio last time . He can afford to drop to 43 percent, and still win, if nonwhite turnout is constant.
- 74 percent: The proportion of white "evangelical/born again" voters won by the McCain-Palin ticket, when they made up 26 percent of the total vote. These voters have never been asked to support a Mormon before. Mormon-baiting turned out to be the dog that didn't bark this year, but we have no great handle, yet, on this aspect of the vote, which will be crucial in the Rust Belt and Virginia.