The Fix has written repeatedly about how no president has ever been re-elected with employment over 7.4 percent, how no Republican has ever won the presidency without winning Ohio and any number of supposed electoral truisms.
Of course, the thing about electoral truisms is that they are only true until they aren't. And, oftentimes the history behind these "it's always been this way and it always will be this way" proclamations is often brief enough to make them less conclusive than they at first appear. (For evidence, read our takedown of the unemployment rate "precedent".)
Today we came across a comic strip on the xkcd blog that tells the danger of relying on electoral precedents better than we ever could. Check it out.