Alan Abramowitz has a post just up at Larry J. Sabato’s Crystal Ball on “Diverging Coalitions: The Transformation of the American Electorate.” His topic is the demographic changes that led to Senator Obama’s election and why President Obama can push a more progressive agenda than other recent Democratic presidents.
While it is no revelation that Obama benefitted from the rapid growth of the non-white population of the U.S. in recent years, Abramowitz sheds fresh light on the dramatic increase in non-white voters, including,

…it has accelerated in the last quarter century. It is a result of increased immigration from Asia, Africa and Latin America, higher birth rates among minority groups, and increased registration and turnout among African-Americans, Hispanics, and other nonwhite citizens. Moreover, this shift is almost certain to continue for the foreseeable future based on generational differences in the racial and ethnic composition of the current electorate and Census Bureau projections of the racial and ethnic makeup of the American population between now and 2050.
…In the 16 years between 1976 and 1992, the nonwhite share of the U.S. electorate increased only slightly–going from 11 percent to 13 percent. However, in the 16 years between 1992 and 2008 the nonwhite share of the electorate doubled, going from 13 percent to 26 percent. Helped by an aggressive Democratic registration and get-out-the-vote campaign in African-American and Hispanic communities, the nonwhite share of the electorate increased from 23 percent in 2004 to 26 percent in 2008 with African-Americans going from 11 percent to 13 percent, and Hispanics going from 8 percent to 9 percent.

Regarding strategy inside the poltiical parties, Abramowitz adds,

…Along with liberal whites, nonwhite voters constitute the electoral base of the modern Democratic Party while conservative whites constitute the electoral base of the modern Republican Party….Moreover, evidence from national exit polls indicates that both parties’ base voters have become more loyal over the past 32 years. In 1976, Jimmy Carter received only 74 percent of the vote from white liberals and nonwhites while in 1992 Bill Clinton received 81 percent and in 2008 Barack Obama received 85 percent. Similarly, in 1976, Gerald Ford received only 73 percent of the vote from white conservatives while in 1992 George H.W. Bush received 82 percent and in 2008 John McCain received 89 percent.

Moderate whites are stil a key constituency for Dems, explains Abramowitz:

Moderate whites are the swing voters in presidential elections. They generally split their votes fairly evenly between the Democratic and Republican candidates, shifting slightly toward one side or the other depending on short-term factors. According to the 2008 national exit poll, Barack Obama received 53 percent of the vote among moderate whites. This was similar to the results for other newly elected Democratic presidents: Jimmy Carter received 49 percent of the vote of this group while Bill Clinton received 57 percent.

Abramowitz crunches the data and sees a profound change in the Dems’ base:

The Democratic base has gone from the smallest of the three voter groups in 1976 to by far the largest in 2008. When Jimmy Carter was elected in 1976, moderate whites made up 45 percent of voters, conservative whites made up 30 percent, and liberal whites and nonwhites combined made up only 25 percent. Sixteen years later, when Bill Clinton was elected, these proportions had changed only slightly–moderate whites made up 43 percent of voters, conservative whites made up 27 percent, and liberal whites and nonwhites combined made up 30 percent. By 2008, however, the electorate looked very different–conservative whites still made up 27 percent of voters but moderate whites made up only 32 percent, and liberal whites and nonwhites combined made up 44 percent.

In addition to the base, he notes a transformation of the “electoral coalition” that undergirds the Democratic party:

Evidence from the American National Election Studies displayed in Table 3 shows that over time the Democratic electoral coalition has become less white and more liberal while the Republican electoral coalition has become less moderate and more conservative. Moderate-to-conservative whites made up 59 percent of Jimmy Carter’s electoral coalition, but they made up only 33 percent of Barack Obama’s electoral coalition. And conservative whites made up only 48 percent of Gerald Ford’s electoral coalition but they made up 61 percent of John McCain’s electoral coalition.

In terms of policy, Abramowitz believes “President Obama cannot afford to ignore the views of moderate-to-conservative white voters,” but he will likely “pursue a more liberal policy agenda than earlier Democratic presidents” who were more anchored by “the support of moderate-to-conservative whites.”