As expected, both Democratic candidates cruised to wins in two primary contests last night. Hillary Clinton won Kentucky by 35 points, while Obama leads Hillary by 16 in Oregon with 88% of the precincts reporting from the mail-in balloting. To no one’s great surprise, the exit polling shows significant polarization among whites and blacks, apparently extending the identity-politics meltdown in the Democratic Party.

But is that the real story? The Washington Post notes that Obama did much better among whites in Oregon, and points out the reason why:

Kentucky’s Democratic electorate proved tailor-made for Sen. Hillary Rodham Clinton, as her most reliable voters turned out in large numbers, giving her a win of better than 2 to 1 over Sen. Barack Obama. But Obama scored a rare double-digit win among white voters in Oregon, capitalizing on that state’s more liberal electorate.

In Kentucky, white women — core Clinton supporters — made up half of all Democratic primary voters, and whites without college degrees made up 59 percent. According to the network exit poll, Clinton beat Obama by overwhelming margins among both groups, and she carried those age 65 and older by 60 percentage points, her second-best showing among older voters in any of the primaries or caucuses so far.

Obama scored sporadic wins among these voters in previous contests, but in Oregon, a swing state in the 2000 and 2004 presidential elections, a telephone survey of voters in the mail-only Democratic primary showed him doing well among Clinton’s base.

In Oregon, Obama scored his first victory among white voters since March 4, in Vermont. In both Oregon and Vermont, about six in 10 Democratic voters described themselves as liberal. By contrast, liberals made up fewer than four in 10 election-day voters in Kentucky. Clinton won white voters in Kentucky by 49 percentage points.

The common thread appears more ideological than racial, and Oregon and Vermont tend to prove it. Both states have more liberal voters than in the South and the Rust Belt. Exit polling shows 57% of all Democrats voting in the primary self-identify as liberals, with only 13% identifying as conservative; only 37% identified as liberal in Kentucky. Oregon’s electorate tends towards the activist Left, driven by energy from college communities — exactly the kind of demographic that suits Obama.

If true, the problems for Obama in a general election may be even greater than thought. Had the split in the Democratic Party merely been racial, one could have expected a rapprochement in the fall, as the party unified to face off against a center-right candidate in John McCain. Now, though, we can understand the high percentages of voters who say they will vote McCain rather than Obama if Hillary loses the nomination in terms of an ideological response. They see McCain as closer to their political positions. The reaction is not that of a sore loser, but a response to the hard-Left leanings of Barack Obama.

That kind of split will be harder to heal, and perhaps not addressable through a skillful selection of a running mate. McCain has an opportunity to attract votes from Democrats who fear that their party has shifted too far to the left and who fear that Obama is the second coming of Jimmy Carter.