The lesson we take from Senator Clinton's strong victory in Pennsylvania's Democratic primary, which came even after she was outspent by a wide margin, is that Senator Obama has plenty of weaknesses as a candidate. It is hard to win elections in America, even within the Democratic primary electorate, while expressing contempt for guns and religion, while associating with angry radicals like William Ayers and the Reverend Jeremiah Wright, while promising to meet with President Ahmadinejad, and while promising to raise the payroll tax. Mrs. Clinton threw all these issues plus a television commercial featuring Osama bin Laden at Mr. Obama in Pennsylvania, and it worked.

That's good news for those who are hoping for a Republican victory in November, because by pursuing these lines of attack against Mr. Obama, Mrs. Clinton legitimizes them for use by Senator McCain if Mr. Obama holds on to his overall lead to become the eventual Democratic nominee. If, on the other hand, Mrs. Clinton uses the momentum from Pennsylvania to win the nomination, her method would almost certainly require using superdelegates to overrule the preference of the delegates chosen in primaries and caucuses. That process could well alienate the African-American voters who are an important Democratic constituency, and put them in play in November's general election, a dynamic for which Mr. McCain seems to be preparing with his visit this week to Selma. Either way, it's good news for the Republicans that voters in places such as Pennsylvania are learning to look past Mr. Obama's soaring rhetoric to the substantive flaws with his candidacy.