One thing many people haven’t noticed about Hillary Clinton’s 55% to 45% victory over Barack Obama in the Pennsylvania primary is that it put her ahead of Obama in the popular vote. Her 214,000-vote margin in the Keystone State means that she has won the votes, in primaries and caucuses, of 15,112,000 Americans, compared to 14,993,000 for Mr. Obama.

If you add in the votes, as estimated by the folks at realclearpolitics.com, in the Iowa, Nevada, Washington, and Maine caucuses, where state Democratic parties did not count the number of caucus-attenders, Mrs. Clinton still has a lead of 12,000 votes.

Moreover, she may be able to maintain that lead, despite an expected Obama victory in North Carolina on May 6, by rolling up big popular vote margins in West Virginia on May 13, Kentucky on May 20, and Puerto Rico on June 1. So it’s likely that Mrs. Clinton will be able to argue that undecided superdelegates should heed the will of the people.

Obama supporters can counter that claim with arguments of their own. Their candidate is ahead and will remain ahead in delegates chosen in caucuses and primaries. Michigan, where Mr. Obama was not on the ballot, and Florida have been disqualified by the Democratic National Committee for voting too early. Counting popular votes unduly discounts the results from caucuses, in which many fewer people participate than in primaries. And the Democratic Party can’t afford to alienate the young and black voters who enthusiastically back Mr. Obama.

These arguments will probably prevail. Yet Mrs. Clinton’s popular vote lead is one piece of evidence that suggests that Mr. Obama will be a weak general election candidate. In national polls, neither Democrat seems stronger than the other: The realclearpolitics.com average of polls as this is written shows Mr. Obama leading John McCain 46% to 45% and Mrs. Clinton and Mr. McCain tied at 46% apiece. But they don’t run the same in different states.

SurveyUSA’s 50-state polls released in March showed that electoral votes would go to different parties in 15 states depending on whether Mr. McCain was pitted against Mrs. Clinton or Mr. Obama. And it is electoral votes that determine who will be president.

There are states where Mr. Obama runs stronger than Mrs. Clinton. They include most of the West — notably Colorado, a state Democrats lost in 2000 and 2004 but which has trended their way since. They include states in the Upper Midwest, like Minnesota, and New England states like Connecticut and New Hampshire, which Democrats won in 2004 but where Mrs. Clinton seems weak.

But Mrs. Clinton seems to run stronger than Mr. Obama in the industrial (or formerly industrial) belt, running west from New Jersey through Pennsylvania and Ohio to Michigan and Missouri. Mr. 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.

Mr. 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% of the vote in Broward County and 62% in Palm Beach County — both have large Jewish populations. In this year’s Florida primary, Mr. Obama lost those counties to Mrs. Clinton by 57% to 33% and 61% to 27%. No Democrat can carry Florida without big margins in Broward and Palm Beach.

Mr. 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 Reverend 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 superdelegates 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.