Missouri has voted for the winner in all but two presidential elections since 1904.

"Show Me State"?? More like "Show Me Who's President State"! This remarkable phenomenon has been nicknamed the "Missouri Bellwether", as a bellwether is an indicator or predictor of something - in this case, politics. The only exceptions to this 'rule' have been the elections of 1956 and 2008. In '56, Missouri's electoral votes went to Illinois governor Adlai Stevenson when Dwight D. Eisenhower won in a landslide. More recently, slightly more Missourians voted for Senator John McCain, but then-Senator Barack Obama defied the odds to become our nation's 44th president.

(source)