But Clinton seems to run stronger than Obama in the industrial (or formerly industrial) belt, running west from New Jersey through Pennsylvania and Ohio to Michigan and Missouri. Obama's weakness among white working-class voters in the primaries here suggests he is poorly positioned to win votes he will need to carry these states in November. This is not a minor problem -- we're talking about 84 electoral votes.

Obama has also fared poorly among Latino and Jewish voters in every primary held so far. This is of consequence most notably in Florida, which has 27 electoral votes. In 2000, Al Gore won 67 percent of the vote in Broward County and 62 percent in Palm Beach County -- both have large Jewish populations. In this year's Florida primary, Obama lost those counties to Clinton by 57 percent to 33 percent and 61 percent to 27 percent. No Democrat can carry Florida without big margins in Broward and Palm Beach.

Obama's weakness among Latinos and Jews could conceivably put California's 55 electoral votes in play. Los Angeles County delivered an 831,000 vote plurality for John Kerry in 2004. Most of that plurality came from areas with large numbers of Latinos and Jews.

Barack Obama's 20-year association with his "spiritual mentor," the Rev. Jeremiah Wright, his "friendly" relationship will unrepentant Weather Underground bomber William Ayers and his remark that "bitter" small-town Pennsylvanians "cling to guns and religion" do not help him with any of these key voting groups. And his discomfort, evident in the Pennsylvania debate, when he is greeted with anything but adulation does not augur well for his ability to stand firm and show a sense of command in the face of the stringent criticism he is bound to receive as the Democratic nominee.

Hillary Clinton's current and tenuous popular vote lead may not persuade Democratic super-delegates to reject the candidate who has, after all, won more delegates in primaries and caucuses. But it may prompt some to think hard about Electoral College arithmetic.