It's worth mentioning that in 2012 Romney had an advantage with high propensity suburban voters in the key swing states, but still lost to Obama's low propensity coalition despite much lower turnout than 2008.
A lot of the narratives about 2008 & 2012 that were prevalent at the time were overturned, or at very least called into question, by later research. A big part of Obama's coalition was high propensity non-evangelical white working class voters, especially in the Midwest, who McCain and Romney were terrible fits for and who he knew how to talk to.
