A look at 2012 Demographics

Myself and others speculated that if the GOP won white voters by about 20 points or more, that would offset any gains for Democrats from white turnout being held at 2008 levels (when they made up 74% of the electorate). And indeed, Romney performed much better among white voters than John McCain four years earlier, winning the largest voting block 59-39%. McCain only carried the group by 12%.

But what many did not count on (myself included) was a full 2% drop in the number of white voters in the electorate. That, coupled with 2008-like African American turnout, increased Latino turnout, and a stronger Obama margin with Latinos led to Romney's demise.
 Here is the national popular vote, extrapolated from the 2012 Exit poll race/ethnicity numbers:

Race/ethnicity        Obama                     Romney

72% white              28.08   (39%)           42.48  (59%)
13% black              12.09   (93%)            0.78   (6%)
10% Latino             7.1      (71%)            2.7      (27%)
3%  Asian               2.19    (73%)            0.78    (26%)
2%  Other               1.16     (58%)           0.76     (38%)
                                50.62 %                    47.5 %

Looking at the race/ethnicity exit polling breakdown alone, it appears Barack Obama carried the national popular vote by about 3 points, 51-48% when rounded. Compare these numbers to what they would have looked like if turnout resembled the 2008 electorate's racial/ethnic composition.

2012 exit poll numbers reweighted to 2008's racial/ethnic composition:

Race/ethnicity        Obama                     Romney

74% white              28.86   (39%)           43.66  (59%)
13% black              12.09   (93%)            0.78   (6%)
9% Latino              6.39      (71%)           2.43    (27%)
2%  Asian               1.46    (73%)            0.52    (26%)
3%  Other               1.74     (58%)           1.14     (38%)
                                50.54 %                    48.53 %

The result indicates that the GOP's issue is not running up huge double-digit leads with white voters because, clearly, that's not enough. Even if the composition of the electorate had resembled the slightly more white, less Hispanic 2008 electorate, Obama would have led 51-49%, based on 2012 exit polling.  You have to go all the way back to 2004 to find an electorate that would get Romney a win. That year, the electorate was 77% white, and less African American and Latino.

2012 exit poll numbers reweighted to 2004's racial/ethnic composition:

Race/ethnicity        Obama                     Romney

77% white              30.03   (39%)           45.43  (59%)
11% black              10.23   (93%)            0.66   (6%)
8% Latino              5.68      (71%)           2.16      (27%)
2%  Asian               1.46    (73%)            0.52    (26%)
2%  Other               1.16     (58%)           0.76     (38%)
                                48.56 %                    49.53 %

Unfortunately for Republicans, demographic trends do not point to any 77% white presidential electorates in the future. In fact, the 72% figure will likely be lower in 2016. Seems pretty clear where Republicans have to do better. That doesn't necessarily mean compromise their principles. But it certainly requires more extensive outreach.