Why do Democrats do so poorly with white voters?

As this chart shows, Barack Obama won reelection with just 39% of the white vote. Note that Bill Clinton did no better in 1992. More telling; white guys Walter Mondale in ‘84, Jimmy Carter in ‘80 and George McGovern in ‘72 all did more poorly than Obama. It’s also important to note that the white vote as a total percentage of the US electorate has declined significantly from 1972 to 2012, and this decline is expected to continue into the foreseeable future.

Why do Democrats perform poorly with the white vote? What could they do to build support in my demographic? And given that they can win handily without white majorities, should they even try to woo whites? Would it require policy changes that might alienate the winning coalition they currently have?

For the background on this issue, see Chris Cillizza and Jon Cohen’s blog entry in the Washington Post.