Soon after the 2008 election I frequently predicted that the state results would largely go closer to 50-50 in the states that President Obama either won by huge margins or lost by huge margins. It was hard to see why President Obama could gain votes in California or New York because he had to be in a max-out position in such states. Likewise I expected the President to convince some or those who voted against him that he was not going to take away their guns and their Bibles.
The extreme polarization of results between the States looked like the anomaly -- one likely to be reversed. I figured that the Republicans would have to come up with RINO types to win back some House and Senate seats... and they did well with Tea Party types this time.
So, you ask, what is the difference between a polarized election and one not so polarized? President Obama won the 2008 election by 7.26%; in 1944 FDR won the election by roughly 7.49% To be sure the historical circumstances were vastly different; America had a clear and shared purpose in 1944 that it lacked in 2008 (and still does), and the incumbent President was already dying. FDR lost one state by 21% (Kansas) and lost only three others by 10% or more. He won all eleven former Confederate states by more than 20% (but those states did not hold free, fair, or competitive elections in those days). The one non-Southern state that he won by more than 20% was -- and you will find this hard to believe -- Utah. He won six other states by 10% or more.
In 1944, 295 electoral votes were decided in free and fair elections by 8% or lesser margins. In 2008 only 116 electoral votes were so decided. So far as I can tell all Presidential elections were fair and honest in all states in 2008.