For better or worse  and many Democrats fear it is for worse  the race goes on.

Senator Hillary Rodham Clinton defeated Senator Barack Obama in Pennsylvania on Tuesday by enough of a margin to continue a battle that Democrats increasingly believe is undermining their effort to unify the party and prepare for the general election against Senator John McCain.

Despite a huge investment of time and money by Mr. Obama and pressure on Mrs. Clinton by the party establishment to consider folding her campaign, she won her third big state in a row. Mrs. Clinton showed again that she is a tenacious campaigner with an ability to connect with the blue-collar voters Mr. Obama has found elusive and who could be critical to a Democratic victory in November.

Mrs. Clinton’s margin was probably not sufficient to fundamentally alter the dynamics of the race, which continued to favor an eventual victory for Mr. Obama. But it made clear that the contest will go on at least a few weeks, if not more. And it served to underline the concerns about Mr. Obama’s strengths as a general election candidate. Exit polls again highlighted the racial, economic, sex and values divisions within the party.

Image Senator Hillary Rodham Clinton and Bill Clinton celebrating her victory in the primary with supporters in Philadelphia. Credit... Jessica Kourkounis for The New York Times

To take one example, only 60 percent of Democratic Catholic voters said they would vote for Mr. Obama in a general election; 21 percent said they would vote for Mr. McCain, exit polls show.