Although it's been amplified recently by the coverage of Barack Obama's remarks in San Francisco (the so-called "Bitter-gate") and the statements of his former pastor Rev. Jeremiah Wright, the issue of appealing to white working-class voters has been a topic of discussion for months.

Putting aside the valid point that white working-class voters have opted for the Republican candidate in general elections -- by margins of consistently more than 15 percentage points -- since 1972, it's apparent that Hillary Clinton is the Democratic candidate of choice among white working-class voters, particularly in states such as Ohio and Pennsylvania. Given that Clinton and Obama are ideologically quite similar, what is the reason behind her significantly greater appeal to white working-class voters? And how can Obama gain the support of those voters over John McCain -- even if only to keep the margin to ten percentage points or less?

Harold Meyerson, Op-Ed columnist for the Washington Post, believes that reaching out to union members is key. He quotes compelling statistics from previous elections regarding the margins between union and non-union voters:

"White male union members gave Kerry 57 percent of their vote; white male nonmembers, 38 percent - a 19-point gap. Fifty-seven percent of white male union members who didn't go to college voted for Kerry, while only 34 percent of white male, non-union non-collegians backed him - a 23-point gap."

In other words, union membership was the determining factor for many white male voters, not college education. Unions "remind their members what's at stake...that the Democratic candidate's support for universal health care, managed trade, green-collar jobs and more affordable college is what the nation needs." Meyerson advocates using Working America -- an AFL-CIO-run program that operates "in white working-class neighborhoods of key swing states, signing people up not for workplace representation but for certain union benefits -- and to enlist them in the federation's political program" as a means of drumming up support for Obama among white working-class voters, whether they are union members or not.

A Huffington Post interview with Democratic strategist David "Mudcat" Saunders gets even more specific as to the salient difference between Clinton and Obama in this area. Saunders, "who preaches the importance of recruiting rural whites, suggests that politically strategic blunders are to blame, including, most prominently, allowing Sen. Hillary Clinton to define herself as an anti-trade candidate."

But James Edmund Pennington (pen name) puts forth a more controversial theory in a March 21 essay in American Thinker; namely, that Obama's losses to Clinton among white working-class voters are rooted in racial demographics. That is, "in settings where the two races deal more directly with each other, and get to know each other better, through shared public schools, workplaces, public conveyances, universities, etc., they seem to like each other less, not more."

As evidence, he cites the differences in demographics and voting patterns in Wisconsin (won by Obama) and Ohio (won by Clinton):

"In Wisconsin more than 75% of the black population resides in the Milwaukee area, a metropolitan area that accounts for only 32% of Wisconsin's total population. This means that in Wisconsin the white portion of 68% of the state's population (which is more heavily white than the state as a whole because of the concentration of blacks in Milwaukee) rarely if ever encounters blacks. Thus, for a high proportion of Wisconsin whites, blacks are abstractions, approached most closely by turning on Oprah.

Now consider Ohio: to begin with, the black population, in percentage terms, is nearly double that of Wisconsin (11.5% versus 5.7%). But its dispersion within and among the white population is the real difference between the two states' racial demographics. In Ohio 80% of the state's 11.3 million residents reside in the eight largest metropolitan areas (Columbus, Cleveland, Cincinnati, Toledo, Akron, Dayton, Youngstown and Canton). These cities contain, in the order listed, 24%, 51%, 43%, 24%, 28%, 43%, 44% and 21% black residents. Thus, in Ohio a very high percentage of the white population, particularly its working class component, has regular contact with blacks, or, if living in outer suburbs, has direct contact with other whites who do.

The widely disparate residential patterns of the races is obvious: in Wisconsin, the vast majority of whites live, work, shop, and send their children to school in a world that includes few if any blacks; in Ohio the reverse is true, and the races regularly brush up against each other in all these categories of daily life."

Pennington acknowledges that in the isolated comparison of Wisconsin and Ohio, correlation does not imply causation. But he goes on to note that "without exception, the Wisconsin pattern (little interracial contact) and the Ohio pattern (much more such contact) have correlated with identically opposite results throughout the Clinton/Obama battles: every state outside the South where Obama carried the white vote and won the primary or caucus was one with a small to negligible black population (Wyoming, Vermont, Wisconsin, Maine, Washington, Nebraska, Minnesota, Kansas, Utah, North Dakota, Idaho, Alaska and Iowa); in every state where a substantial and widely dispersed black population regularly interacts with whites, Obama lost the white vote and lost the primary: Texas, Ohio, Rhode Island, California, New Jersey, and Massachusetts." He considers the prevalence and consistency of this pattern sufficient evidence to support his theory as to why Obama has not won - and will not win in the general election -- these traditional battleground states.

While I agree that history indicates that it's unlikely that the Democratic candidate -- be it Clinton or Obama -- will carry the white working-class vote, I tend to side with Meyerson over Pennington in terms of the reasons why. I don't deny that race is still a divisive issue in America, particularly in some parts more than others, but I can't accept a single pattern as conclusive evidence.

So what is the substance of Clinton's appeal over Obama among white working-class voters? Based on exit polls, it seems that "experience" has trumped "change" as the key priority in those states where Clinton has won (and where she has carried older voters, women, and white working-class voters). Obama admitted as much after the Pennsylvania primary. Also, Clinton is viewed as a known quantity, whereas Obama is an uncertainty. And while Bill Clinton's stump speeches on Hillary's behalf have been anathema to some voters, it's his presidential legacy -- and his white working-class roots -- that attract many others.