Alan Abramowitz, a political scientist who follows voting trends most carefully, writes:
The fact that Democratic identifiers now decisively outnumber Republican identifiers means that in order to win, Democrats only have to unite and turn out their own base. If Obama wins the national popular vote by even a single percentage point, it's worth remembering, he'll almost certainly win the electoral vote as well. In order for John McCain to win, on the other hand, Republicans not only have to unite and turn out their own base, which they have been fairly successful at doing in recent elections, but they also have to win a large majority of the small bloc of true independents and make significant inroads among Democratic identifiers, which they have not been very successful at doing recently.
In other words -- it doesn't really matter if Barack Obama isn't doing as well among white working class Dems as Hillary Clinton is. He doesn't need their votes to win.
A big part of the reason for the growing Democratic edge in party identification is the fact that Democrats now enjoy a large advantage among voters under the age of 30, as well as among African American and Hispanic voters. All three of these groups have been turning out in record numbers in the Democratic primaries, and there is no reason to believe that they will not also turn out in large numbers in November. Based on the early indicators of voter interest, the 2008 presidential election could very well witness the highest turnout of eligible voters in the postwar era, and that can only be good news for Democrats. With a unified Democratic Party, a clear message of change, and a strong grass-roots effort at mobilizing the Democratic base, on January 20, 2009, Barack Obama will be taking office as the head of a unified Democratic government. And John McCain will still be a member of the minority party in the United States Senate.