Political scientist Alan Abramowitz has written an interesting piece on demography and politics. Briefly summarized, usually the Republicans win among white voters, although the margin varies from year to year, but Democrats always win the nonwhite vote in a landslide.
Projections out to 2020 are fairly accurate because anyone who will be of voting age in 2020 was born in 2002 or later and those data are known. In addition, if immigration continues unabated, the percentage of nonwhites is only likely to increase because many of the immigrants are legal and nonwhite and they tend to become citizens 5-10 years after arrival.

The Republicans’ base of (older) white voters is shrinking and the Democrats base of (younger) nonwhite voters is growing. This means that unless the Republicans can figure out how to capture a larger piece of the nonwhite vote, they have a big problem coming up. And poll after poll has shown that the Republicans main policy positions–lower taxes and smaller government–are extremely unpopular with nonwhite voters, who want a larger, more activist government. If the Republicans don’t change their policies, they are unlikely to pickup many new voters in the nonwhite demographic, but if they do change their policies, they may alienate their base. If they win big in 2010, as seems likely now, they may fall into a trap of thinking they are doing the right thing and just continue doing it, when the real reason for a possible big win in 2010 is the historical near-certainty of the voters being disappointed with the Party in charge.