[O]ur conversations with Democrats who speak to the Clintons make plain that their public comments are only the palest version of what they really believe: that if Obama is the nominee, a likely Democratic victory would turn to a near-certain defeat. Far from a no-holds-barred affair, the Democratic contest has been an exercise in self-censorship. Rip off the duct tape and here is what they would say:

Obama has serious problems with Jewish voters (goodbye Florida), working-class whites (goodbye Ohio) and Hispanics (goodbye, New Mexico).

Republicans will also ruthlessly exploit openings that Clinton — in the genteel confines of an intraparty contest — never could. Top targets: Obama’s radioactive personal associations, his liberal ideology, his exotic life story, his coolly academic and elitist style.

Vandehei and Harris report:

But one argument seems indisputably true: Obama is on the brink of the Democratic nomination without having had to confront head-on the evidence about his general election challenges.

They interviewed many Democrats for the article:

Skepticism about Obama’s general election prospects extends beyond Clinton backers. We spoke to unaffiliated Democratic lawmakers, veteran lobbyists, and campaign operatives who believe the rush of enthusiasm for Obama’s charisma and fresh face has inhibited sober appraisals of his potential weaknesses.

Obama's two greatest potential liabilities:

Assuming voting patterns evident in the nominating contest continue into the fall, Obama would be vulnerable if McCain can approximate the traditional GOP performance in key states.

....Stories about Obama’s Chicago associations with 1960s radicals Bernardine Dohrn and William Ayers landed with barely a ripple. So, too, did questions about whether he once backed a total ban on handguns (he says no but in a 1996 state legislative race his campaign filled out a questionnaire saying yes). Obama’s graceful handling of the Rev. Jeremiah Wright controversy may have turned that into a net positive against Clinton. But all this was in a Democratic contest. What about about when Obama’s running against a Republican?

The reporters examine each one in turn. They acknowledge that African American and college- educated upscale white voters will come out in droves in November and be a big boon to him.

But there is reason to question whether he would be able to perform at average levels with other main pillars of the traditional Democratic coalition: blue-collar whites, Jews and Hispanics. He has run decently among these groups in some places, but in general he’s run well behind her.

Obama lost the Jewish vote by double-digits in Florida, New York and Maryland — and that was before controversy over anti-Israel remarks of Wright. An undecided Democratic superdelegate told us many Jewish voters are itching for a reason to break with the party and side with Republicans, who have embraced the Israeli cause with passion. A small shift could swing swing states like Florida and Pennsylvania, which have significant Jewish populations.

On the Hispanic vote, they note Obama won only 1/3 of it on Super Tuesday and even less in Texas:

A Democratic nominee needs big margins with Hispanics to win states like New Mexico, California, Colorado and Arizona. In the fall, Obama would be running against a Republican with a record on immigration that will resonate with Hispanics.

On the poor, rural and blue collar voters:

Three out of every four blue-collar whites in small towns and rural areas of Ohio voted for Clinton over Obama on March 4. The reality is, this is already an electorate with deep cultural divisions — and that’s in the Democratic Party.

On to issue-based attacks:

McCain, by contrast, would have a free hand to exploit a paper trail showing Obama’s evolution — opponents would say reversals — over the past decade from liberal positions on gun control, the death penalty and Middle East politics. He would exploit Obama’s current position in favor of driver’s licenses for illegal immigrants and beginning diplomatic talks with U.S. adversaries like the dictators of Iran and Venezuela. Will those issues help lower-income white voters “come back together” with Obama?

It will be the Republicans using the kitchen sink approach to attack Obama, including playing on falsities and engaging in baseless character attacks.

Here will be the real kitchen sink: every damaging comment or association from Obama’s past, mixed together with innuendo and downright fiction, to portray him as an an exotic character of uncertain values and weak patriotism.

Obama’s advisers say they are not naive about freak show attacks. Their response is that Obama’s appeal to a new brand of politics, and his personal poise and self-confidence, will allow him to transcend attacks and stereotypes in ways that Gore and Kerry could not.

Obama is indeed poised and self-confident. But the current uproar over his impromptu sociology lesson in San Francisco about “bitter” voters in Pennsylvania raise questions about his self-discipline, and his understanding of how easy it is for a politicians in modern politics to lose control of his or her public image.

Compared to Hillary:

Clinton has her own baggage, to put it mildly. But it’s been rummaged through for years, so what Democrats see is pretty much what they would get.