In order to cheer up Democrats after yesterdays setback, I will simulate the 2052 presidential election.
Imagine a republican that does roughly as well as George Bush did in 2004, and receives:
58% of Non-Hispanic White vote
12% of African-Americans vote
40% of Hispanics vote
40% of Asians and others vote
In 2008 landscape that would have been enough for a bare majority of the vote.
But the population structure is changing, mainly due to immigration. The census bureau has projections of the population structure. Now imagine that we are in the 2052 Presidential election, and the republican receives the same vote for each population group as Bush did. I also use census bureau data on voting patterns (they have the best data).
Let us assume that Hispanics and Asians close only half the gap in turnout with African Americans, as more become citizens and more of the citizens become politically engaged. (They don't close the gap entirely, because as this group will still be young and foreign born in 2052. African American turnout in 2008 was unusually high because of the Obama effect.)
Because of change of the demographic composition a Republican with the Bush 2004 winning share for each population group, enough for 50.3% in 2008, would get only 46.8% of the vote in 2052, close to McCain's losing share!
The median voter model predicts Republicans would somehow respond to this. But that model is overly simplistic, there is no guarantee that they will or even can. In Sweden between 1932-2010 Social Democrats were in power 85% of the time, in contrast to the simple prediction of the median voter theorem.
Unless Republicans sharply move to the left or the voters to right, today's result is just a temporary setback. Democrats only need to be a little more patient.