Here are the demographics of Obama and Romney voters:
White voters accounted for 88% of Romney's support and 56% of Obama's. Their share of the country is declining by about 2 percentage points with every presidential election.
Latino, Black, and Asian voters accounted for 10% of Romney's support and 42% of Obama's. Their share of the country is growing by about 2 percentage points with every presidential election, with Latinos accounting for three-fifths of that growth.
That first graph was the GOP's present demographics problem. This, from Pew, is the future.
In 1988, Michael Dukakis lost the white vote by 19 points and won 111 electoral votes. In 2012, Barack Obama lost the white vote by a worse margin -- 20 points -- and tripled Dukakis with 332 electoral votes. Country's changing.