Identity politics has been a subtext (and a often a supertext) of the race between Clinton and Obama. This is, in effect, the only way to interpret the age / gender / racial voting patterns so far. Depending on the underlying demographics, they become more or less pronounced from state to state, but they are omni-present.

Underlying this is the following intuition: people like to associate with and vote for candidates with whom they identify, i.e., people they perceive to be like them. Obama is fundamentally similar to three demographics: blacks, men, and the affluent middle class. His campaign, until the Wright affair came up, was able to make him appeal to all of these groups, without making his black identity too salient to white men or white folks of the affluent middle class. The Wright affair made his black identity salient. While Obama also identifies with the affluent middle class - just as strongly, only a (very?) small minority of white people have much familiarity with black culture. Hence, showing aspects of that culture is scary - it reminds people that Obama, in part, is not like them.

The campaign had to address this. Obama is affluent, male and black. He is now explaining to us why this is an asset. In a sense, the takeaway from Obama's speech is "I am also like you and that's because I have shared experiences with all of you". It is a complex and nuanced message - and it will take some time to see if it was well received.

Given that Obama is the more talented politician, Clinton's only strategy has been to make Obama either corrupt (didn't work so well), inexperienced (working a little bit, but not very well), or not like you (working well). This is why it is good for the Clinton campaign to make the discussion about race. The more we think about Obama's blackness, the more white people think "OMIGOD! he's not like me!" - and also why Obama rushed to change the subject today with his foreign policy speech.

Clinton, for her part, actively pushes identity politics. For example, in her stump speech she often mentions how great it is that the two Democratic finalists are a woman and an African American. The reason she does this is because there are more women than blacks - and hence she is then simultaneously reminding more voters that she is like them and Obama is not - then the other way around. This is a highly cynical, scorched earth, strategy.

If Clinton is nominated, it will be because a plurality (or at least a perceived plurality) of voters were afraid of voting for someone not like them. The same holds for McCain in the general. Obama's path to the presidency requires him to neutralize the race issue.

A footnote: I recognize and respect that not everyone is influenced by identity politics - but enough are that Obama's losing ground in the polls.