SENATOR Hillary Rodham Clinton’s victory last week in the Pennsylvania presidential primary bought Mrs. Clinton time, but it’s what might fill the time that troubles Democrats: an increasingly sharp dialogue between core Democratic constituencies — blacks and a wide swath of women. Will either of those constituencies leave their grievances at home come November? Will large numbers stay home altogether if their history-making candidate loses the nomination? The reassurances, and the warnings, are flying. Howard Dean, chairman of the Democratic National Committee, Senate Majority Leader Harry Reid and House Speaker Nancy Pelosi have all promised a resolution shortly after the...